Dog Mitral Valve Disease ACVIM Stage Calculator

Mitral Valve Disease – The Most Common Heart Disease In Dogs

Myxomatous mitral valve disease (MVD), also called endocardiosis, is the most common acquired heart disease in dogs — accounting for about 75% of all canine acquired cardiac disease (Atkins 2009). It predominantly affects small breeds, with Cavalier King Charles Spaniels having the highest prevalence — approximately 50% by age 5 and 95% by age 11.

The disease is a degeneration of the mitral valve leaflets that prevents complete closure, allowing blood to regurgitate back into the left atrium during systole. Over time this enlarges the left atrium and ventricle, raises pulmonary venous pressure, and eventually produces congestive heart failure (CHF) with pulmonary oedema.

The ACVIM 2019 staging system (Keene et al.) is the international standard for canine MVD management. This calculator applies the system and translates each stage into the evidence-based treatment plan.

The ACVIM Stages

Stage	Definition	Treatment
A	At-risk breed, no murmur, no disease	None — annual auscultation
B1	Murmur, no cardiac enlargement	None
B2	Murmur + cardiac enlargement (asymptomatic)	Pimobendan per EPIC trial
C	History of CHF	Multi-drug therapy
D	Refractory CHF	Escalation, hospice planning

Stage A – At-Risk Breed

The breeds most affected:

• Cavalier King Charles Spaniel (the standout — essentially 100% lifetime prevalence)
• Miniature Poodle / Toy Poodle
• Dachshund
• Chihuahua
• Yorkshire Terrier
• Pomeranian
• Maltese
• Shih Tzu
• Bichon Frise
• Papillon
• Miniature Schnauzer
• Boston Terrier

Treatment: None. Annual cardiac auscultation at routine vet visits catches the first murmur. For Cavaliers especially, breed-club cardiac screening schemes in the UK and Denmark have been shown to slow disease progression in screened lines.

Stage B1 – Murmur Without Enlargement

The asymptomatic murmur stage. Auscultation reveals a left apical systolic murmur (usually starting as Grade 1-2/6 and progressing over time), but imaging (echocardiogram or radiographs) shows no cardiac enlargement.

Treatment: None. The EPIC trial showed that pimobendan does not benefit Stage B1 dogs; ACE inhibitors do not delay CHF onset in Stage B. Re-imaging every 6-12 months catches progression to B2.

Action items:

• Establish a baseline resting respiratory rate (RRR) — knowing the dog’s personal RRR baseline matters for catching progression to Stage C
• Routine echocardiogram or chest radiograph every 6-12 months
• Annual auscultation for murmur progression

Stage B2 – The Turning Point

This is the most important stage in canine cardiology because it’s where evidence-based intervention begins.

Definition: Murmur + cardiac enlargement on imaging:

• Echocardiogram: LA/Ao ratio ≥1.6 AND LVIDDN (normalised left ventricular internal diameter in diastole) ≥1.7
• Or radiograph: vertebral heart size (VHS) ≥10.5-11 depending on breed

The EPIC Trial

Boswood et al. 2016 (JVIM) — the EPIC (Evaluation of Pimobendan in Dogs with Cardiomegaly caused by preclinical MMVD) trial — showed:

• Pimobendan started at Stage B2 delayed onset of CHF by approximately 15 MONTHS
• Median time to CHF or cardiac-related death: 1228 days on pimobendan vs 766 days on placebo
• Well-tolerated with minimal side effects

This is one of the strongest evidence-based interventions in canine cardiology. Any dog confirmed at Stage B2 should start pimobendan unless contraindicated.

Stage B2 Treatment

• Pimobendan 0.25-0.3 mg/kg orally q12h (twice daily)
• Empty stomach preferred — give 1 hour before food
• No other cardiac medication routinely needed at this stage
• Daily home RRR monitoring begins here
• Re-imaging every 6-12 months

Stage C – Symptomatic CHF

History of overt congestive heart failure — pulmonary oedema, dyspnoea, lung crackles, cough, exercise intolerance. May be acute (presenting in respiratory distress) or chronic (currently controlled on medication).

Acute CHF Treatment

• Oxygen supplementation
• Furosemide 2-4 mg/kg IV q4-8h until stable
• Pimobendan 0.25-0.3 mg/kg q12h (or higher acute initial dose if not already on)
• Sedation if very anxious (butorphanol)
• ICU monitoring typically required

Chronic Stage C Multi-Drug Regimen (Lifelong)

1. Furosemide 1-3 mg/kg PO q12-24h — lowest dose that prevents CHF recurrence
2. Pimobendan 0.25-0.3 mg/kg q12h — inotrope + vasodilator
3. ACE inhibitor — benazepril 0.25-0.5 mg/kg q24h, or enalapril 0.5 mg/kg BID
4. Spironolactone 2 mg/kg q24h — potassium-sparing diuretic + RAAS blockade

This four-drug regimen is the standard of care for Stage C MVD globally. Monitor renal function and electrolytes every 1-3 months.

Optional Additions

• Torsemide — more potent loop diuretic; can replace furosemide in refractory cases
• Hydrochlorothiazide — sequential nephron blockade for diuretic resistance
• Sildenafil — for pulmonary hypertension complicating CHF
• Antiarrhythmic — sotalol, mexiletine, amiodarone for specific arrhythmias

Stage D – Refractory CHF

Signs of heart failure persist despite maximum standard therapy. The dog is on full multi-drug regimen but still has pulmonary oedema, breathing difficulty, or other CHF signs.

Escalation Options

• Increase furosemide dose to ceiling
• Switch to torsemide (more potent loop diuretic)
• Add hydrochlorothiazide for sequential nephron blockade
• Add sildenafil if pulmonary hypertension present
• Antiarrhythmics for refractory arrhythmias

Cardiology Referral

If not already involved. Specialist input can identify unrecognised contributing factors and optimise therapy.

Quality of Life Focus

Stage D is end-of-life territory. The PuppaDogs Quality of Life Calculator implements the 7-domain Villalobos framework — useful for these conversations. Hospice planning and end-of-life decision-making become central.

Home Resting Respiratory Rate (RRR) Monitoring

The single most useful home tool for owners of dogs with Stage B2 or C MVD. RRR is the rate at which the dog breathes during sleep or calm rest.

Why It Matters

Schober 2010, Porciello 2016, and the EPIC trial all confirmed:

• Sustained RRR above 30 breaths/min OR
• 20-25% above the dog’s personal baseline

…often predicts decompensation before overt clinical signs. Catching the rise early means catching CHF early — diuretic adjustment can prevent crisis.

How To Measure

• Wait until the dog is sleeping or calmly resting
• Not panting (panting is invalid as RRR)
• Count chest rises (one rise + one fall = one breath)
• 30 or 60 seconds, multiply to get per-minute rate
• Daily during Stage B2 and C

PuppaDogs has a dedicated Resting Respiratory Rate Calculator with detailed thresholds and interpretation.

Diet And Lifestyle

Low-Sodium Diet

Supports CHF management:

• Hill’s h/d
• Royal Canin Cardiac
• Purina CV
• All low-sodium with adequate potassium and omega-3

Restrict salty treats; check ingredient lists.

Weight Management

Obesity dramatically worsens CHF outcomes. Maintain ideal body weight (BCS 5). If overweight at diagnosis, controlled gradual weight loss is appropriate.

Exercise

Continue moderate, predictable exercise — Stage B2 dogs benefit from normal activity. Avoid extremes (intense exercise, hot weather). Stage C dogs continue gentle exercise as tolerated.

Omega-3 Supplementation

Modest cardiac evidence in canine DCM/AF; reasonable adjunct in MVD. Combined EPA+DHA 40-100 mg/kg/day. The PuppaDogs Omega-3 Calculator details dosing.

Cavalier King Charles Spaniel – Special Considerations

Essentially 100% lifetime prevalence if the dog lives long enough. The breed-specific picture:

• Median age of murmur onset: 6-7 years
• Median age of CHF onset: 10-11 years
• Earlier onset than non-CKCS dogs by ~2-3 years
• Concurrent syringomyelia common (separate disease, neurological signs)
• UK and Danish breed-club cardiac screening schemes have shown reduced disease progression in screened lines

Annual cardiac auscultation from age 4-5 in CKCS catches the first murmur, and echocardiographic screening at age 5 is reasonable for breed-club-encouraged screening.

Mitral Valve Repair Surgery

Now available at a small number of specialist veterinary centres globally (notably Japan — Dr Masami Uechi — and a few UK and US centres). The procedure:

• Open-heart surgery with cardiopulmonary bypass
• Repair of the mitral valve (not replacement)
• Potentially curative in selected dogs
• Expensive: typically GBP 15,000-30,000 / USD 20,000-40,000
• Mortality risk 5-15% peri-operatively
• Selection criteria: appropriate stage, no major comorbidities, good general health

For owners of CKCS or other affected breeds where finances allow, discuss with a veterinary cardiologist if interested. The field is rapidly developing.

Dilated Cardiomyopathy – Different Disease

Important caveat: dilated cardiomyopathy (DCM) is a different disease, predominantly affecting large breeds:

• Doberman Pinscher
• Great Dane
• Boxer (typically arrhythmogenic right ventricular cardiomyopathy)
• Newfoundland
• Irish Wolfhound
• Cocker Spaniel (taurine-deficient form)

DCM has separate ACVIM consensus guidelines and different management. If your dog has been diagnosed with DCM rather than MVD, this calculator does not apply.

Honest Caveats

• Definitive staging requires veterinary examination — auscultation for murmur grade, echocardiogram or radiographs for enlargement.
• Owner-reported signs are approximate — vets find more findings than owners report.
• EPIC trial benefit (Stage B2 pimobendan) is one of the most replicated findings in canine cardiology — start pimobendan if confirmed Stage B2.
• Treatment varies by individual — drug choices, doses, and combinations depend on the whole clinical picture.
• This calculator helps you understand the staging and discuss management with your vet; it does not replace cardiology assessment for complex cases.

Conclusion

Mitral valve disease is the most common canine acquired heart disease, predominantly affecting small breeds (above all the Cavalier King Charles Spaniel). The ACVIM 2019 staging system (A → D) is the international standard and drives every meaningful treatment decision. The EPIC trial established that pimobendan started at Stage B2 delays CHF onset by approximately 15 months — one of the strongest evidence-based interventions in canine cardiology. Daily home RRR monitoring is the most useful tool for catching progression early. With modern multi-drug therapy, many Stage C dogs live months to years of good-quality life. For Cavaliers and other high-risk breeds, annual cardiac screening from middle age identifies disease at the stages where intervention pays back most.

Frequently Asked Questions

What is mitral valve disease in dogs?

Mitral valve disease (MVD), also called myxomatous mitral valve disease or endocardiosis, is the most common acquired heart disease in dogs – accounting for about 75% of canine acquired cardiac disease. It’s a degeneration of the mitral valve leaflets that prevents complete closure, allowing blood to regurgitate back into the left atrium during systole. Over time this enlarges the heart and eventually produces congestive heart failure. Predominantly small breeds; Cavalier King Charles Spaniels essentially 100% lifetime prevalence.

What are the ACVIM stages of canine mitral valve disease?

ACVIM 2019 staging: Stage A = at-risk breed (CKCS, Mini Poodle, Dachshund, etc.) with no murmur, no treatment needed. Stage B1 = murmur but no cardiac enlargement, no treatment. Stage B2 = murmur + cardiac enlargement (LA/Ao>=1.6, VHS>=10.5-11), start pimobendan per EPIC trial. Stage C = history of CHF, multi-drug therapy (furosemide + pimobendan + ACE inhibitor + spironolactone). Stage D = refractory CHF, escalation + hospice planning.

What is the EPIC trial for dog heart disease?

The EPIC trial (Boswood 2016, Journal of Veterinary Internal Medicine) is one of the most practice-changing canine cardiology studies. It showed that starting pimobendan 0.25-0.3 mg/kg twice daily at ACVIM Stage B2 (asymptomatic mitral valve disease with cardiac enlargement) DELAYED the onset of congestive heart failure by approximately 15 MONTHS. Median time to CHF or cardiac death was 1228 days on pimobendan vs 766 days on placebo. Any dog confirmed at Stage B2 should start pimobendan.

What medications are used for dogs with CHF?

Stage C (history of CHF) lifelong multi-drug regimen: (1) FUROSEMIDE for diuresis – acute pulmonary oedema 2-4 mg/kg IV q4-8h, long-term 1-3 mg/kg PO q12-24h. (2) PIMOBENDAN 0.25-0.3 mg/kg q12h – inotrope + vasodilator. (3) ACE INHIBITOR (benazepril 0.25-0.5 mg/kg q24h, or enalapril 0.5 mg/kg BID). (4) SPIRONOLACTONE 2 mg/kg q24h – potassium-sparing diuretic + RAAS blockade. Monitor renal function and electrolytes every 1-3 months.

Why is daily breathing rate monitoring important for heart disease dogs?

Resting respiratory rate (RRR) is the most useful home monitoring tool for dogs with Stage B2 or C mitral valve disease. The Schober 2010 / Porciello 2016 / EPIC trial evidence shows that a sustained RRR above 30 breaths/min OR 20-25% above the dog’s personal baseline often predicts developing or worsening CHF BEFORE overt clinical signs – giving the vet a window to adjust diuretics or other medication before crisis. Daily home counts (sleep or calm rest, NOT panting) take 30 seconds and can prevent emergencies.

Which dog breeds get mitral valve disease most often?

Most affected breeds: Cavalier King Charles Spaniel (essentially 100% lifetime prevalence – the standout); Miniature Poodle and Toy Poodle; Dachshund; Chihuahua; Yorkshire Terrier; Pomeranian; Maltese; Shih Tzu; Bichon Frise; Papillon; Miniature Schnauzer; Boston Terrier – predominantly small breeds. For Cavaliers especially, breed-club cardiac screening schemes (UK, Denmark) have been shown to slow disease progression in screened lines. Annual cardiac auscultation from age 4-5 in CKCS is sensible.

Related PuppaDogs Calculators

Continue building your dog’s personalised care plan with these related PuppaDogs calculators:

• Dog Pregnancy / Whelping Due-Date Calculator
• Puppy Weight Predictor (Adult Weight Calculator)
• Heatstroke Risk Calculator for Dogs
• Bloat (GDV) Risk Calculator for Dogs
• Dog Life Expectancy Calculator (Breed, Body Condition, Lifestyle)
• Spay/Neuter Timing Calculator for Dogs (Breed-Specific)

References & Further Reading

The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.

1. Keene BW, Atkins CE, Bonagura JD, et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. JVIM, 2019.
2. Boswood A, Haggstrom J, Gordon SG, et al. Effect of pimobendan in dogs with preclinical myxomatous mitral valve disease and cardiomegaly: The EPIC Study. JVIM, 2016.
3. Atkins C, Bonagura J, Ettinger S, et al. Guidelines for the diagnosis and treatment of canine chronic valvular heart disease. JVIM, 2009.
4. Schober KE, Hart TM, Stern JA, et al. Detection of congestive heart failure in dogs by Doppler echocardiography. JVIM, 2010.
5. Porciello F, Rishniw M, Ljungvall I, et al. Sleeping and resting respiratory rates in dogs and cats with medically controlled left-sided congestive heart failure. The Veterinary Journal, 2016.
6. Haggstrom J, Boswood A, O’Grady M, et al. Effect of pimobendan or benazepril hydrochloride on survival times in dogs with congestive heart failure – the QUEST study. JVIM, 2008.
7. PuppaDogs. Resting Respiratory Rate Calculator and Omega-3 Calculator. puppadogs.com.