Myxomatous Mitral Valve Disease (MMVD)

What you might notice

• A heart murmur your veterinarian hears through the stethoscope - often the only finding, and often years before your dog feels any different
• Breathing faster than usual while genuinely asleep or resting quietly, which is the earliest sign most owners can actually spot at home
• Tiring sooner on the usual walk, stopping to rest, or lagging behind when they never used to
• Breathing that looks like effort - the belly pumping with each breath, elbows pushed out, or a dog who will not settle lying flat
• Coughing - but read this one carefully: in dogs with this disease, a cough is more often caused by an enlarged heart pressing on the airway above it, or by separate airway disease, than by fluid in the lungs
• Restlessness or pacing at night, or wanting to sit up rather than lie down
• A brief faint or wobble, usually lasting only seconds, most often while excited, coughing or straining
• Gradual loss of muscle over the back and hind legs even though your dog is eating much the same amount
• A belly that looks rounder or fuller than usual, which points to the right side of the heart also being involved

Standard of care

1. Stage the dog with echocardiography and radiography before writing any prescription

   Approved / guideline-backed

   The ACVIM 2019 system has five stages: A (predisposed breed, no murmur, no disease), B1 (asymptomatic murmur, heart not enlarged enough to meet the treatment criteria), B2 (asymptomatic murmur WITH cardiomegaly meeting the criteria below), C (MMVD severe enough to cause current OR PAST clinical signs of heart failure - which includes right-sided failure with ascites, not only pulmonary oedema; dogs stay stage C after their signs resolve on treatment), and D (heart failure refractory to standard stage C therapy, in practice needing more than 8 mg/kg/day of furosemide or the equipotent torsemide dose alongside standard doses of the other drugs). The B2 criteria - ideally all of them - are murmur intensity >= 3/6, LA:Ao >= 1.6, LVIDDN >= 1.7, and VHS > 10.5; the approved pimobendan label states B2 cardiomegaly is diagnosed on meeting all three imaging criteria (VHS > 10.5 AND LA:Ao >= 1.6 AND LVIDDN >= 1.7) in a dog with a moderate or loud mitral murmur. Nothing else in this protocol can be applied correctly without the stage, and the stage cannot be assigned by stethoscope. Staging is not only about who gets treated: the label contraindicates pimobendan in stage A and B1, and in hypertrophic cardiomyopathy and aortic stenosis, so the echocardiogram is also what rules OUT the dogs in whom the drug is the wrong drug. This is where the honest commercial message sits: for MMVD the thing a dog actually needs bought for it is the diagnostic workup.

   ACVIM Specialty of Cardiology consensus panel; recommendations graded by quantity and quality of available evidence. Consensus guideline, dog.

   Keene BW, Atkins CE, Bonagura JD, Fox PR, Haggstrom J, Luis Fuentes V, Oyama MA, Rush JE, Stepien R, Uechi M. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med. 2019;33(3):1127-1140. PMID 30974015. DOI 10.1111/jvim.15488. Stage C definition verbatim from that guideline: 'Stage C dogs have MMVD severe enough to cause current or past clinical signs of heart failure.' Label criteria: FDA-approved VETMEDIN (pimobendan) chewable tablet label, NADA 141-273, PRECAUTIONS section.

2. Stage B2: pimobendan, which is the one intervention proven to delay the onset of heart failure

   Approved / guideline-backed

   The EPIC study randomised 360 client-owned dogs with preclinical MMVD and cardiomegaly (LA:Ao >= 1.6, LVIDDN >= 1.7, VHS > 10.5), on no other cardiovascular medication, to pimobendan 0.4-0.6 mg/kg/day in divided doses or placebo. Median time to the composite primary endpoint of onset of CHF, cardiac death or euthanasia was 1228 days (95% CI 856-NA) on pimobendan versus 766 days (667-875) on placebo (P = .0038), hazard ratio 0.64 (0.47-0.87) - a prolongation of the preclinical period of roughly 15 months. Dogs on pimobendan also lived longer (median survival 1059 days versus 902 days, P = .012), and adverse events did not differ between groups. ACVIM dosing for B2 is 0.25-0.3 mg/kg PO q12h (Class I, strong evidence). This is the number to quote to an owner deciding whether the echo is worth paying for.

   Named products: Pimobendan. FDA-approved for this exact indication: 21 CFR 520.1780 (chewable tablets) and 21 CFR 520.1782 (oral solution), verbatim indication - 'For the delay of onset of congestive heart failure in dogs with Stage B2 preclinical myxomatous mitral valve disease.' Sponsors 000010 (Boehringer Ingelheim Animal Health USA) and 069043. The VETMEDIN chewable-tablet label states 'Approved by FDA under NADA # 141-273'. A conditionally approved pimobendan entry for the same B2 indication also exists at 21 CFR 516.1780. LABEL CONTRAINDICATIONS, verbatim: 'Do not administer VETMEDIN in cases of hypertrophic cardiomyopathy, aortic stenosis, or any other clinical condition where an augmentation of cardiac output is inappropriate for functional or anatomical reasons.' and 'Do not administer VETMEDIN to dogs with Stage A or B1 preclinical MMVD due to the risk of cardiac pathology associated with exaggerated hemodynamic responses to VETMEDIN.' LABEL PRECAUTIONS: safety has not been evaluated in dogs younger than 6 months of age, dogs with congenital heart defects, dogs with diabetes mellitus or other serious metabolic diseases, dogs used for breeding, or pregnant or lactating bitches; safety is not established in asymptomatic heart disease of other causes, or in CHF from causes other than MMVD or DCM; and pimobendan has not been evaluated in stage B2 dogs already receiving other heart medications. Human warning on the label: 'Not for use in humans. Keep this and all medications out of reach of children. Consult a physician in case of accidental ingestion by humans.' Federal (USA) law restricts this drug to use by or on the order of a licensed veterinarian.

   Prospective, randomised, placebo-controlled, blinded, multicentre clinical trial in 360 dogs with naturally occurring preclinical MMVD; the highest level of evidence available for any intervention in this disease (dog).

   Boswood A, Haggstrom J, Gordon SG, Wess G, Stepien RL, Oyama MA, Keene BW, Bonagura J, MacDonald KA, Patteson M, et al. Effect of pimobendan in dogs with preclinical myxomatous mitral valve disease and cardiomegaly: the EPIC study - a randomized clinical trial. J Vet Intern Med. 2016;30(6):1765-1779. PMID 27678080. DOI 10.1111/jvim.14586

3. Stage B1, or a murmur with no cardiomegaly: no cardiac medication is indicated - and say so plainly

   Approved / guideline-backed

   This is a negative recommendation and it belongs on a client-facing page as clearly as on a clinician-facing one. For stage B1 there is no randomised evidence FOR any cardiac drug and none AGAINST one either - the absence runs in both directions and must be stated that way. EPIC did not enrol B1 dogs, the approved indication is written for B2, and the approved US pimobendan label goes further than silence: it contraindicates administration to stage A and B1 dogs 'due to the risk of cardiac pathology associated with exaggerated hemodynamic responses'. So for pimobendan in B1 the position is not merely unproven, it is label-contraindicated. Separately - and this is a DIFFERENT population, not B1 evidence - the DELAY study randomised 184 dogs with preclinical MMVD to spironolactone plus benazepril or placebo, and every enrolled dog met the ACVIM B2 echocardiographic criteria (LA:Ao >= 1.6 AND LVEDDn >= 1.7). DELAY failed its primary endpoint: median time to heart failure or cardiac death was 902 days on treatment versus 1139 days on control (P = 0.45). The treated group did show lower VHS, LA:Ao, LVEDDn, E-peak velocity and NT-proBNP at study end, so the drugs did something to the remodelling; they did not demonstrably delay the outcome the owner cares about. Importing DELAY as evidence about B1 dogs would repeat, in the opposite direction, exactly the population error this page warns about with EPIC. The correct B1 plan is a recheck interval, an owner taught to count sleeping respiratory rate, and honesty that many B1 dogs never progress to needing drugs.

   Named products: Pimobendan is CONTRAINDICATED by its FDA-approved US label in stage A and B1 preclinical MMVD; it is not merely off-label there. Spironolactone plus benazepril as a delay-of-progression strategy is not supported in preclinical disease: it failed its primary endpoint in B2-criteria dogs (DELAY) and has never been tested in B1 dogs.

   Stage B1: no randomised controlled trial of any cardiac drug in this population was located - the absence of evidence is stated as an absence, and is reinforced by an explicit label contraindication for pimobendan in stage A/B1. DELAY: prospective, randomised, multicentre, single-blinded, placebo-controlled trial, n=184, ALL meeting stage B2 echocardiographic criteria, primary endpoint not met (dog).

   Borgarelli M, Ferasin L, Lamb K, Bussadori C, Chiavegato D, D'Agnolo G, Migliorini F, Poggi M, Santilli RA, Guillot E, et al. DELay of Appearance of sYmptoms of Canine Degenerative Mitral Valve Disease Treated with Spironolactone and Benazepril: the DELAY Study. J Vet Cardiol. 2020;27:34-53. PMID 32032923. DOI 10.1016/j.jvc.2019.12.002 (enrolment criteria LA:Ao >= 1.6 and LVEDDn >= 1.7 per the published abstract). Label contraindication: FDA-approved VETMEDIN (pimobendan) label, NADA 141-273, CONTRAINDICATIONS section.

4. Stage C: a loop diuretic plus pimobendan plus an ACE inhibitor plus spironolactone

   Approved / guideline-backed

   ACVIM home therapy for stage C is four drugs, all Class I, but at sharply different levels of evidence on the panel's own scoring - print both, because 'Class I' alone flattens a real difference: pimobendan 0.25-0.3 mg/kg PO q12h (Class I, LOE STRONG); furosemide, commonly 2 mg/kg PO q12h titrated to the lowest effective dose (Class I, LOE MODERATE); spironolactone 2.0 mg/kg PO q12-24h (Class I, LOE MODERATE); and an ACE inhibitor - enalapril or benazepril 0.5 mg/kg PO q12h (Class I, LOE WEAK), the weakest leg of the regimen by the panel's own grading. The pimobendan component is supported head-to-head: in QUEST, 252 analysed dogs in CHF from MMVD were randomised to pimobendan or benazepril on top of conventional therapy, and median time to the composite endpoint of cardiac death, euthanasia for heart failure or treatment failure was 267 days on pimobendan versus 140 days on benazepril (hazard ratio 0.688, 95% CI 0.516-0.916, P = .0099). Sustained oral furosemide at or above 8 mg/kg/day (or the equipotent torsemide dose) in the face of appropriate doses of the other three drugs defines progression to stage D. For atrial fibrillation the panel uses diltiazem with digoxin for rate control - and note that spironolactone reduces digoxin elimination and raises digoxin concentrations, so that combination needs digoxin monitoring.

   Named products: Pimobendan (FDA-approved for clinical CHF due to MMVD or DCM; 21 CFR 520.1780 and 520.1782; VETMEDIN label NADA 141-273) - see the B2 step for its full contraindications. Furosemide (FDA-approved for use in dogs, oral, 21 CFR 520.1010). Spironolactone with benazepril as a fixed-combination chewable tablet is FDA-approved as CARDALIS, 21 CFR 520.2138, sponsor 013744, 'Approved by FDA under NADA # 141-538', verbatim indication - 'With concurrent therapy (e.g., furosemide, etc.) for the management of clinical signs of mild, moderate, or severe congestive heart failure in dogs due to atrioventricular valvular insufficiency (AVVI)'. ITS LABEL CONTRAINDICATIONS, verbatim: 'Do not administer CARDALIS in conjunction with non-steroidal anti-inflammatory drugs (NSAIDs) in dogs with renal insufficiency. Do not administer CARDALIS to dogs with hypoadrenocorticism (Addison's Disease), hyperkalemia, or hyponatremia. Do not administer CARDALIS to animals with known hypersensitivity to ACE inhibitors or spironolactone.' Its PRECAUTIONS require renal function and serum potassium to be evaluated before starting and monitored regularly because of increased hyperkalaemia risk; require adequate hydration in any dog given an NSAID alongside it; warn about digoxin (spironolactone raises digoxin concentrations) and DOCP (opposing mechanism); advise caution in hepatic dysfunction; state that safety has not been evaluated in GROWING dogs (spironolactone is antiandrogenic) and 'has not been established in pregnant, lactating or breeding dogs'; and state that 'The safety and effectiveness of concurrent therapy of CARDALIS with pimobendan has not been evaluated' - which is worth saying out loud, because the ACVIM regimen does combine them. Enalapril and benazepril as single agents are widely used in dogs; individual approval numbers for every single-agent product were not verified in this pass and must be confirmed against animaldrugsatfda.fda.gov before publication. ACE inhibitors as a class are fetotoxic and should not be used in pregnant or breeding animals.

   QUEST: prospective, single-blinded, randomised, reference-controlled multicentre trial, 260 enrolled / 252 analysed (dog). Stage C regimen composition and grading from the ACVIM consensus panel: pimobendan Class I/LOE strong, furosemide Class I/LOE moderate, spironolactone Class I/LOE moderate, ACE inhibitor Class I/LOE weak.

   Haggstrom J, Boswood A, O'Grady M, Jons O, Smith S, Swift S, Borgarelli M, Gavaghan B, Kresken JG, Patteson M, et al. Effect of pimobendan or benazepril hydrochloride on survival times in dogs with congestive heart failure caused by naturally occurring myxomatous mitral valve disease: the QUEST study. J Vet Intern Med. 2008;22(5):1124-1135. PMID 18638016. DOI 10.1111/j.1939-1676.2008.0150.x; ACVIM stage C regimen: Keene BW et al. J Vet Intern Med. 2019;33(3):1127-1140. PMID 30974015. DOI 10.1111/jvim.15488

5. Torasemide once daily is a legitimate alternative to twice-daily furosemide

   Controlled trial in this species

   The TEST analysis pooled two prospective, randomised, single-blinded, reference-controlled trials in 366 dogs with CHF from degenerative mitral valve disease: torasemide q24h (n=180, median 0.24 mg/kg/day) versus furosemide q12h (n=186, median 1.39 mg/kg q12h), each added to standard CHF therapy over three months. Torasemide was non-inferior on the primary success criterion in both studies, and was associated with a two-fold reduction in the risk of reaching the composite cardiac endpoint of spontaneous cardiac death, euthanasia for heart failure or worsening CHF class (adjusted HR 0.47, 95% CI 0.27-0.82, P = 0.0077). Two honest caveats: the trials were single-blinded and industry-sponsored, and the composite-endpoint advantage was a secondary criterion, so the defensible claim is non-inferiority plus a favourable secondary signal - not established superiority. THE DOSES ARE NOT INTERCHANGEABLE AND THIS IS A SAFETY POINT, NOT A PHARMACOLOGY FOOTNOTE: the reason 0.24 mg/kg/day sits next to 1.39 mg/kg q12h is that torsemide is roughly 10 to 20 times as potent as furosemide per milligram. ACVIM substitutes torsemide at 1/10 to 1/20 - about 5% to 10% - of the furosemide dose, approximately 0.1-0.3 mg/kg q24h. A mg-for-mg swap at a pharmacy, in a pill organiser or by a well-meaning owner is a massive overdose. The torsemide label also forbids giving the two loop diuretics together. 'Torasemide' (the INN used in the European literature) and 'torsemide' (the US product name) are the same drug.

   Named products: Torsemide oral solution is CONDITIONALLY approved by FDA for dogs as UpCard-CA1, 21 CFR 516.2475, sponsor 017030 (Vetoquinol USA); the label states verbatim 'Conditionally approved by FDA pending a full demonstration of effectiveness under application number 141-577.' Verbatim indication - 'for use with concurrent therapy with pimobendan, spironolactone, and an angiotensin converting enzyme (ACE) inhibitor for the management of pulmonary edema in dogs with congestive heart failure caused by myxomatous mitral valve disease (MMVD).' Conditional approval means FDA found it safe and with a reasonable expectation of effectiveness while the sponsor completes effectiveness data collection; it requires annual renewal. Saying 'FDA-approved' without the word conditionally would be inaccurate. LABEL CONTRAINDICATIONS: do not use in dogs with renal failure, anuria, severe dehydration, hypovolaemia or hypotension; 'Do not administer UpCard-CA1 concomitantly with other loop diuretics (e.g., furosemide).'; avoid in known hypersensitivity to torsemide or the excipients. LABEL WARNINGS/PRECAUTIONS: 'Not for use in humans.'; it can cause electrolyte imbalance, dehydration and plasma volume reduction, 'enhancing the risk of circulatory collapse, thrombosis, and embolism'; it 'is not indicated for dogs presenting in acute crisis'; pre-existing electrolyte abnormalities must be corrected first; bloodwork at 24 and 48 hours after dosing and then monthly; 'Concurrent use of non-steroidal anti-inflammatory drugs (NSAIDs) with UpCard-CA1 may result in a decreased natriuretic response and renal impairment'; safety not evaluated in breeding dogs, pregnant or lactating bitches, or dogs with diabetes.

   Two prospective randomised single-blinded reference-controlled trials, pooled, n=366 dogs with naturally occurring disease (dog).

   Chetboul V, Pouchelon JL, Menard J, Blanc J, Desquilbet L, Petit A, Rougier S, Lucats L, Woehrle F. Short-term efficacy and safety of torasemide and furosemide in 366 dogs with degenerative mitral valve disease: the TEST study. J Vet Intern Med. 2017;31(6):1629-1642. PMID 28975664. DOI 10.1111/jvim.14841

6. Write down the things that must not happen: no human medicines, no NSAIDs, no owner dose changes, no routine drip without warning

   Approved / guideline-backed

   Every one of these is a documented label or guideline restriction, not caution for its own sake. (1) NSAIDs: the FDA-approved spironolactone/benazepril label contraindicates concurrent NSAIDs in dogs with renal insufficiency and requires adequate hydration in any dog given both; the conditionally approved torsemide label warns that concurrent NSAIDs 'may result in a decreased natriuretic response and renal impairment'; and ACVIM lists concurrent NSAID use among the recognised causes of diuretic resistance. An ACE inhibitor plus a loop diuretic plus an NSAID is the classic triple combination for acute kidney injury, and osteoarthritis is near-universal in the 9.5-year-old small dogs this page describes - so the arthritis plan has to be made deliberately, with renal values checked, and with non-NSAID options considered first. (2) Human medicines: owners must be told explicitly never to give ibuprofen, naproxen, aspirin or acetaminophen/paracetamol, never human heart or cough medicine, and never another pet's prescription, particularly another pet's diuretic. Never give a canine NSAID to a cat: cats are deficient in hepatic glucuronidation and acetaminophen/paracetamol in particular is potentially lethal in a cat. (3) Owner dose changes: every dog managed at home on a diuretic needs a written instruction to CALL BEFORE CHANGING ANYTHING - no skipping, doubling, stopping or 'just one extra' water tablet without speaking to the clinic, because both directions of error (fluid overload and dehydration with azotaemia) present as a dog who looks worse. (4) Anaesthesia and intravenous fluids: a stage C dog can be tipped into pulmonary oedema by routine intravenous fluids for a dental or a lump removal, so the owner must tell any treating team about the heart disease and the drug list BEFORE any sedation, anaesthetic or drip. (5) All four cardiac drugs named on this page are prescription-only - federal (USA) law restricts them to use by or on the order of a licensed veterinarian - and nothing on this page substitutes for physical examination, imaging and staging by that veterinarian.

   Named products: Contraindicated or hazardous combinations named on approved labels: NSAIDs plus spironolactone/benazepril in renal insufficiency (contraindicated); NSAIDs plus torsemide (reduced natriuresis, renal impairment); torsemide plus another loop diuretic such as furosemide (contraindicated); spironolactone plus digoxin (raised digoxin concentrations); spironolactone plus DOCP (opposing mechanisms). Human analgesics - ibuprofen, naproxen, aspirin, acetaminophen/paracetamol - have no place in this protocol in either species.

   Label contraindications and precautions from the FDA-approved CARDALIS (spironolactone/benazepril, NADA 141-538) and VETMEDIN (pimobendan, NADA 141-273) labels and the conditionally approved UpCard-CA1 (torsemide, application 141-577) label; diuretic-resistance causes including concurrent NSAID use from the ACVIM consensus guideline (dog).

   FDA-approved labels: VETMEDIN (pimobendan) chewable tablets, NADA 141-273; CARDALIS (spironolactone/benazepril hydrochloride) chewable tablets, NADA 141-538; UpCard-CA1 (torsemide) oral solution, conditionally approved under application number 141-577 - all as published on DailyMed. Diuretic resistance and NSAIDs: Keene BW et al. J Vet Intern Med. 2019;33(3):1127-1140. PMID 30974015. DOI 10.1111/jvim.15488

7. Teach the owner to count sleeping respiratory rate, and act on it

   Controlled trial in this species

   This is the cheapest, most useful intervention in the whole disease and it costs nothing. In 51 dogs with stable, medically well-controlled left-sided CHF, owner-measured median sleeping respiratory rate was 20 breaths/min (range 7-39); eight dogs averaged 25 or more and only one dog averaged 30 or more. Dogs with subclinical heart disease also average under 30. Rates were stable day to day, and canine sleeping rate was unrelated to diuretic dose or to pulmonary hypertension. The practical rule is to establish each dog's own baseline while they are well and to treat a sustained rise above that personal baseline as the trigger for a call - a dog whose usual 18 becomes a consistent 32 has changed, even though 32 is not a dramatic number; a sustained rise of roughly a quarter above that dog's own baseline is the usual working threshold. But every dog must also be given a NUMBER, because many dogs are never baselined: in the absence of a personal baseline, a sleeping respiratory rate that stays above about 30 breaths/min warrants a call. That 30 is a conventional backstop derived from these reference data (only 1 of 51 medically controlled CHF dogs averaged 30 or more, and subclinical dogs average under 30), not a prospectively validated cut-off, and it should be described that way. Resting rates run higher and noisier than sleeping rates (canine median 24, range 12-44, with seven of 51 dogs at 30 or more), so the two must not be judged against the same threshold.

   Prospective owner-measured study, 51 dogs and 22 cats with stable medically controlled left-sided CHF (dog and cat data reported separately in the source; only the canine figures are used here).

   Porciello F, Rishniw M, Ljungvall I, Ferasin L, Haggstrom J, Ohad DG. Sleeping and resting respiratory rates in dogs and cats with medically-controlled left-sided congestive heart failure. Vet J. 2015;207:164-168. PMID 26639825. DOI 10.1016/j.tvjl.2015.08.017

8. Diet in stage B2: mild sodium restriction and a palatable diet with adequate protein and calories

   Controlled trial in this species

   ACVIM for stage B2, quoted in full rather than as a fragment: 'Principles guiding dietary treatment at this stage include mild dietary sodium restriction and provision of a highly palatable diet with adequate protein and calories for maintaining optimal body condition.' That recommendation is Class IIa on WEAK evidence. Note what is NOT in the stage B2 dietary recommendation: omega-3 fatty acids are not recommended for asymptomatic B2 dogs by this guideline, and no other nutraceutical is recommended at this stage at all. A diet plan that makes an asymptomatic heart dog eat less is the wrong plan.

   ACVIM consensus panel, stage B2 dietary recommendation, Class IIa, LOE weak (dog).

   Keene BW et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med. 2019;33(3):1127-1140. PMID 30974015. DOI 10.1111/jvim.15488

9. Diet in stage C: hold the calories, restrict sodium modestly, and consider omega-3 only in the dogs the guideline names

   Controlled trial in this species

   The stage C dietary recommendations are separate from the B2 ones and stronger. Maintain adequate calorie intake - the panel puts maintenance in stage C at approximately 60 kcal/kg body weight - and use simple culinary strategies to improve appetite (Class I, LOE moderate). Ensure adequate protein and avoid low-protein renal diets unless severe concurrent renal failure is present (Class I, LOE moderate). Modestly restrict sodium counting sodium from ALL sources, including treats, table food and the food used to hide tablets (Class I, LOE moderate). Supplement potassium only if hypokalaemia is identified, which the panel notes anecdotally is much more common on torsemide (Class I, LOE expert opinion). Omega-3 fatty acids appear ONLY here, in stage C, and only as a conditional suggestion, verbatim: 'Consider supplementing with omega-3 fatty acids, especially in dogs with decreased appetite, muscle loss, or arrhythmia' (Class IIa, LOE moderate). That is not a recommendation to put every heart dog on fish oil, and it is not a stage B2 recommendation - presenting it as one is a real misreading that this page previously made. No other nutraceutical received a panel recommendation. Cardiac cachexia - muscle loss despite adequate intake - is a genuine prognostic problem.

   ACVIM consensus panel, stage C dietary recommendations: calories, protein and sodium Class I/LOE moderate; potassium supplementation Class I/LOE expert opinion; omega-3 Class IIa/LOE moderate and conditional on inappetence, muscle loss or arrhythmia (dog).

   Keene BW et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med. 2019;33(3):1127-1140. PMID 30974015. DOI 10.1111/jvim.15488

10. Surgical mitral valve repair - a real option, at a very small number of centres

    Controlled trial in this species

    ACVIM verbatim for stage C: 'In centers with low complication rates, Stage C patients benefit from surgical intervention to repair their mitral valve apparatus' (Class I, moderate evidence). For advanced B2, verbatim: 'Surgical intervention in advanced Stage B2 is possible and recommended by some panelists for clients who can afford and access mitral valve repair at the few centers demonstrating evidence of acceptably low complication rates and effective, durable results' (Class IIa). The scale is now substantial in the highest-volume programmes: 1019 dogs in ACVIM stages B2, C and D underwent repair with artificial chordae and annuloplasty under cardiopulmonary bypass at a single Japanese institution between 2017 and 2020, and no dog required a second repair. Events clustered early - 61 dogs reached the composite outcome of all-cause death, postoperative CHF or surgical revision within 100 days (19.6 events per 1000 dog-months) versus 211 dogs between 100 and 1400 days (7.1 per 1000 dog-months). Stage D dogs carried 2.2 times the daily hazard of an early event compared with stage B2 dogs, and later events were associated with increasing age, higher body weight, Cavalier King Charles Spaniel breed versus Chihuahua, and preoperative tricuspid regurgitant velocity above 3.7 m/s. The two honest caveats: these are single-institution retrospective data with no medically managed comparator arm, and the result is not transferable to a low-volume centre - the guideline conditions its own recommendation on demonstrated low complication rates.

    ACVIM Class I (stage C) and Class IIa (advanced B2) recommendations; supported by large single-centre retrospective cohorts, not by any randomised comparison against medical management (dog).

    Kurogochi K, Furusato S, Takahashi E, Tabata M, Mizuno M, Nii Y, Uechi M. Long-term outcomes of mitral valve repair with artificial chordae and annuloplasty for myxomatous mitral valve disease in dogs. J Vet Intern Med. 2025;39(4):e70171. PMID 40525587. DOI 10.1111/jvim.70171; guideline positions: Keene BW et al. J Vet Intern Med. 2019;33(3):1127-1140. PMID 30974015

11. Identify and manage pulmonary hypertension separately

    Controlled trial in this species

    Pulmonary hypertension secondary to left heart disease is ACVIM group 2, and it is diagnosed by comprehensive assessment - signalment, clinical signs, tricuspid regurgitant velocity and supporting echocardiographic findings across three anatomic sites - rather than by a single velocity number. It changes prognosis, and in the surgical cohort above a preoperative tricuspid regurgitant velocity over 3.7 m/s carried a hazard ratio of 2.5 for late postoperative events. Treatment follows the pulmonary hypertension consensus statement, whose approach is to target the underlying disease first and add PH-specific therapy on top, with monitoring for improvement, stability or progression. Do not treat pulmonary hypertension as a substitute for optimising the left-sided regimen.

    Named products: Phosphodiesterase-5 inhibitors, principally sildenafil, are the agents used in dogs with pulmonary hypertension. These are extra-label in dogs; no FDA-approved canine product for pulmonary hypertension was located in this research pass, and dose and indication must be taken from the consensus statement and the prescribing veterinarian's judgement rather than from an approved label.

    ACVIM multidisciplinary consensus statement; classification and treatment recommendations graded by the panel (dog).

    Reinero C, Visser LC, Kellihan HB, Masseau I, Rozanski E, Clercx C, Williams K, Abbott J, Borgarelli M, Scansen BA. ACVIM consensus statement guidelines for the diagnosis, classification, treatment, and monitoring of pulmonary hypertension in dogs. J Vet Intern Med. 2020;34(2):549-573. PMID 32065428. DOI 10.1111/jvim.15725

12. Investigate a cough on its own merits rather than escalating diuretics

    Controlled trial in this species

    Because congestive heart failure was not a predictor of coughing in 206 dogs with MMVD, while abnormal airway pattern and left atrial enlargement both were, a coughing dog with a murmur needs thoracic radiographs and an airway assessment - not a reflex furosemide increase. Escalating a diuretic in a dog whose cough is bronchial rather than congestive buys dehydration, azotaemia and electrolyte derangement with no benefit. Left atrial enlargement compressing the left mainstem bronchus is itself a mechanical cause of cough in a dog who is not in failure, and that distinction has to be made on imaging.

    Retrospective multicentre analysis of 206 client-owned dogs with full cardiac evaluation including echocardiography and thoracic radiography; univariate and multivariate logistic models (dog).

    Ferasin L, Crews L, Biller DS, Lamb KE, Borgarelli M. Risk factors for coughing in dogs with naturally acquired myxomatous mitral valve disease. J Vet Intern Med. 2013;27(2):286-292. PMID 23398050. DOI 10.1111/jvim.12039

How it is diagnosed

• Careful auscultation is the entry point, not the answer. A left apical systolic murmur in a small older dog raises the suspicion; murmur intensity correlates only loosely with disease severity, and in the ACVIM staging system a murmur of grade 3/6 or louder is one of four criteria for stage B2, never a criterion on its own (Keene et al. 2019, PMID 30974015).
• Echocardiography to separate stage B1 from stage B2 - this is the single decision that determines whether the dog should be medicated. ACVIM thresholds for B2 are left atrial-to-aortic root ratio (LA:Ao) in the right short-axis view in early diastole >= 1.6 and left ventricular internal diameter in diastole normalised for body weight (LVIDDN) >= 1.7. Echocardiography also confirms the lesion is myxomatous mitral disease rather than dilated cardiomyopathy, endocarditis, or a congenital lesion.
• Thoracic radiography for a breed-adjusted vertebral heart score (VHS), where > 10.5 is the radiographic limb of the stage B2 criteria used in EPIC and repeated in the approved pimobendan label, and - separately and just as importantly - to look at the lungs and airways. If echocardiography truly is not available, the label and the ACVIM panel both set a HIGHER radiographic bar: cardiomegaly may be called on radiographs alone only when VHS >= 11.5 and vertebral left atrial size (VLAS) >= 3.0, and if radiographs do not meet both of those, an echocardiogram should be done before starting treatment. Radiography is also how cardiogenic pulmonary oedema is confirmed in a coughing or tachypnoeic dog, and how the very common concurrent airway disease is identified.
• Do not attribute a cough to heart failure by default. In 206 dogs with naturally acquired MMVD, congestive heart failure was NOT a predictor of coughing (OR 1.369, 95% CI 0.723-2.594), whereas an abnormal radiographic airway pattern (OR 3.650, 2.051-6.496) and increased left atrial size measured radiographically (OR 3.637, 1.904-6.950) or echocardiographically (OR 2.553, 1.436-4.539) were significantly associated with it (Ferasin et al., J Vet Intern Med 2013;27:286-92, PMID 23398050, DOI 10.1111/jvim.12039). Treating that cough with escalating diuretics instead of investigating the airway is a common and harmful error.
• Serum creatinine, urea, SDMA where available, electrolytes - potassium specifically - and a urinalysis BEFORE starting a diuretic, an ACE inhibitor or spironolactone, and again after starting them and after every dose escalation. The FDA-approved spironolactone/benazepril label requires renal function and serum potassium to be evaluated before treatment starts and monitored regularly afterwards because of an increased risk of hyperkalaemia; the torsemide label requires bloodwork at 24 and 48 hours after dosing and then monthly. ACVIM advises measuring creatinine, urea and electrolytes 3-14 days after starting furosemide and again 3-14 days after starting an ACE inhibitor, and treats a rise in creatinine of >= 30% above baseline as a reason to be concerned about acute kidney injury. Cardiorenal interaction is the main dose-limiting problem in stage C.
• Systolic blood pressure measurement, both because hypotension changes what can safely be given and because concurrent systemic hypertension changes management.
• NT-proBNP as an adjunct, not a substitute for imaging. It can help decide whether a dyspnoeic dog's problem is cardiac or respiratory, and it was one of the endpoints that moved in the DELAY trial, but no natriuretic peptide cut-off replaces the echocardiographic and radiographic B2 criteria.
• Screen for pulmonary hypertension, which is common in group 2 (left heart disease) form and changes prognosis and drug choice. Tricuspid regurgitant velocity plus supporting echocardiographic findings is the non-invasive route, following the ACVIM pulmonary hypertension consensus statement (Reinero et al., J Vet Intern Med 2020;34:549-573, PMID 32065428, DOI 10.1111/jvim.15725).
• Assess rhythm. Atrial fibrillation and frequent ventricular ectopy both occur in advanced disease and both change treatment. In a 28-dog single-centre surgical series from one high-volume Japanese hospital (10 dogs in whom preoperative atrial fibrillation persisted at 30 days versus 14 that returned to sinus rhythm, with 4 early deaths), 1000-day survival was 45% (95% CI 20-100) with persistent atrial fibrillation versus 90% (95% CI 73-100) with sinus rhythm (P = .030). The direction is clear but the confidence intervals are very wide and the cohort is small and single-centre, so this is a signal, not a survival estimate to quote to an owner (Kurogochi et al., J Vet Intern Med 2026;40(1), PMID 41742514, DOI 10.1093/jvimsj/aalaf028).