Overview

MMVD is chronic myxomatous degeneration and thickening of mitral valve connective tissue. Incomplete closure lets blood flow backward into the left atrium during each ventricular contraction. Over time, the left atrium and ventricle enlarge.

It usually progresses slowly over years, with few or no early symptoms. Regular auscultation and imaging help identify change. Advanced disease raises pulmonary venous pressure and can cause pulmonary edema, a common cardiac emergency.

Predisposed breeds

MMVD can occur in any breed, but is reported earlier and more frequently in:

  • Cavalier King Charles Spaniel — a major predisposed breed, sometimes affected at a young age
  • Maltese, Toy and Miniature Poodles, Yorkshire Terrier, Shih Tzu and Bichon Frise
  • Chihuahua, Dachshund, Miniature Schnauzer and Pomeranian
  • Other older small and medium-sized dogs

Large dogs can also be affected, though less frequently; DCM needs to be distinguished.

What signs should I watch for?

Early MMVD may cause only a murmur. With progression, signs can include:

  • A dry, hacking cough at night or early morning, especially when lying down
  • Repeated increases above the usual sleeping respiratory rate
  • Slow recovery and prolonged panting after gentle walks or stairs
  • Brief loss of consciousness or unsteadiness when excited (syncope)
  • Pale or bluish tongue or gums
  • Reduced appetite, weight loss and low energy

Is every cough caused by the heart?

Small dogs commonly cough from tracheal collapse, chronic bronchitis or lung disease. Cardiac and airway problems may coexist. Auscultation, radiographs and ultrasound together help establish the cause.

Diagnostic steps

Diagnosis combines information gathered in stages rather than one test alone.

  1. Auscultation

    Assess the intensity and location of a left-sided systolic murmur. The Levine grade, from 1 to 6, is a starting point for staging.

  2. Chest X-rays

    Assess vertebral heart score (VHS), left atrial and ventricular enlargement, pulmonary venous congestion and edema.

  3. Echocardiography

    Assess valve shape and thickness, quantify regurgitation with Doppler and measure chamber size for ACVIM staging. Echocardiography is the central diagnostic test.

  4. Blood tests + NT-proBNP

    Kidney and liver function and electrolytes establish a medication baseline. NT-proBNP supports heart failure risk assessment.

  5. Blood pressure measurement

    Noninvasive measurement checks for high or low pressure and helps guide medication choice and dose adjustment.

ACVIM staging

ACVIM classifies MMVD into five stages. The stage determines whether treatment should begin and which medications are appropriate.

Stage Condition When to consider treatment
A Predisposed breed without structural heart changes No medication needed; regular auscultation and examinations recommended
B1 Murmur present without clear heart enlargement Medication not needed; imaging follow-up every 6–12 months
B2 No heart failure symptoms, but left atrial and ventricular enlargement. ACVIM B2 criteria include murmur ≥3/6, LA/Ao ≥1.6, LVIDDN ≥1.7 and breed-adjusted VHS >10.5. Ideally, all four are met and interpreted with individual clinical findings Pimobendan recommended to delay onset of congestive heart failure
C Current or previous heart failure signs, including pulmonary edema or breathing difficulty Combination therapy, including diuretics, inotropes and vasodilators
D Refractory heart failure with reduced response to standard treatment Dose adjustments, additional medications and intensive monitoring

This owner-oriented table summarizes general ACVIM recommendations. The veterinarian applies them to the individual patient.

Treatment and care by stage

The central principle is treatment matched to stage. Starting too early or too late can affect outcomes. We consider both ACVIM stage and the owner's circumstances.

Medication combinations by stage

Pimobendan is recommended for asymptomatic patients meeting B2 criteria to delay congestive heart failure. Diuretics become central at stage C with current or previous congestion such as pulmonary edema. Other medication depends on stage and individual status. Kidney function, electrolytes and blood pressure are monitored.

Home monitoring — Resting respiratory rate (SRR)

Count breaths for one minute while your pet sleeps and compare with the usual rate. Contact the veterinarian if faster breathing recurs and agree on individual contact thresholds. For labored or open-mouth breathing, go straight to the nearest 24-hour emergency veterinary hospital regardless of the count.

Diet and daily care

Sodium restriction depends on stage. Maintain comfortable daily activity and adjust walks in hot or humid weather. Consistent medication times help reduce variation in effect.

Complications and concurrent conditions

Long-term treatment requires monitoring kidney and liver function and electrolytes. Tracheal collapse, chronic kidney disease and endocrine conditions can affect cardiac medication choices and are assessed together.

Frequently asked questions

Should medication start as soon as a murmur is heard?
No. A murmur alone does not determine treatment. Radiographs and ultrasound assess enlargement and ACVIM stage. Pimobendan is recommended when B2 criteria are met; medication is generally not recommended in B1.

Can MMVD be cured?
MMVD is a progressive chronic condition. Treatment aims to slow progression and preserve comfortable daily life rather than promise a cure. Stage-based care can prolong the symptom-free period.

How do I measure SRR?
While your pet sleeps or rests comfortably, count one chest rise and fall as one breath for a full minute. Measure at rest, not just after excitement or exercise.

Will medication be lifelong?
Pimobendan is often used long term in B2. Congestive heart failure at stage C requires additional medication such as diuretics. Choices and doses may change with stage, kidney function, weight and concurrent conditions.

At what age should a predisposed breed be checked?
Predisposed breeds should have auscultation at routine visits regardless of age. Timing and follow-up depend on breed, family history, murmurs and previous results. Confirmed B1 disease is generally reassessed every 6–12 months according to imaging and progression.

What if symptoms suddenly worsen?
For difficult breathing, blue gums or loss of consciousness, go directly to the nearest 24-hour emergency veterinary hospital without waiting for our appointment or social-media response. Pulmonary edema needs prompt stabilization.

References

These external resources explain staging and stage-based management. They do not define our services or an individual prescription.

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