Mitral Valve Disease in Dogs: Stages, Treatment and Home Monitoring

By Dr Duncan Houston

Hearing that your dog has a heart murmur can be frightening. In many older small dogs, the cause is myxomatous mitral valve disease, often shortened to MMVD. A murmur does not, by itself, mean heart failure.

Quick Answer

MMVD gradually changes the valve between the left upper and lower heart chambers, allowing blood to leak backwards. Treatment depends on the stage: some dogs need monitoring, some benefit from medication before symptoms, and dogs with congestive heart failure need a more intensive plan. Monitor sleeping breathing as your vet recommends. Laboured breathing, collapse or blue-grey gums require emergency care.

What a leaking valve does

The heart may compensate for a leak for a long time. With progression, affected chambers can enlarge and pressure can rise enough for fluid to accumulate in the lungs. That fluid accumulation is one form of congestive heart failure.

Cornell's cardiology guidance describes the condition and the signs that can develop. Older small breeds are commonly affected, but size or breed alone cannot confirm the diagnosis.

How the stages guide decisions

The ACVIM consensus guidelines use stages based on disease, heart size and a history of heart failure.

Staging needs appropriate measurements, not simply a louder murmur. A dog whose heart failure is controlled remains a dog with a history of heart failure.

Tests and other possible explanations

A cardiac ultrasound assesses the valve and chamber size. Chest X-rays help evaluate lungs and heart enlargement. Blood pressure, blood tests and an ECG may answer additional questions.

Coughing can also arise from airway disease, infection or other lung problems. Fainting has several possible causes, including rhythm disturbances. Your vet will interpret symptoms alongside examination and test results rather than assume every change comes from MMVD.

Treatment is individual

Medication choices change as disease progresses. Diuretics help remove fluid when heart failure is present; they are not routine treatment for every murmur. Follow-up blood tests can be needed to monitor kidney function and electrolytes. Give medicines on the prescribed schedule and ask before changing a dose.

Valve repair is available at selected specialist centres for suitable patients. Availability, suitability, cost and recovery need a detailed cardiology discussion.

A useful home routine

1. Count breaths when your dog is asleep and not panting or dreaming actively. One rise and fall of the chest is one breath.
2. Record a full minute, or count 30 seconds and double it. Establish a baseline over several calm occasions.
3. Follow your vet's action threshold. A sustained rise from baseline or repeated sleeping rates above about 30 breaths per minute should prompt contact.
4. Track appetite, comfort, exercise tolerance, coughing and medication administration.
5. Attend planned rechecks even when your dog seems well.

Cornell explains the value of recognising breathing changes. An isolated count after activity is less useful than a consistent sleeping trend.

When to seek emergency care

Visible effort to breathe, an extended neck, inability to settle, blue-grey gums, collapse or severe weakness needs immediate assessment. Do not wait to finish a breathing diary. Keep your dog calm, minimise exertion and phone the emergency clinic before travelling. Cornell's respiratory distress guidance describes these warning signs.

Everyday care and common mistakes

Maintain a healthy body condition and discuss suitable activity and diet. Avoid salty extras and unapproved supplements. Do not restrict water because a diuretic increases urination. Avoid forcing exercise when your dog is tired or breathless.

No home measure guarantees prevention of MMVD. Regular examinations, timely staging and a written plan make changes easier to address.

Frequently asked questions

How long can a dog live with MMVD?

The outlook varies widely with stage, progression, other disease and treatment response. A murmur alone cannot predict lifespan.

Does every dog need pimobendan?

No. The decision depends on confirmed stage and individual findings.

Can my dog still walk?

Many can enjoy comfortable activity. Ask your vet for limits appropriate to the current stage.

Does less coughing mean heart failure is cured?

No. Symptoms may improve while the underlying condition still needs treatment and monitoring.

A clear stage, medication schedule and breathing action plan turn an unsettling diagnosis into practical daily care.

For support preparing for a cardiology discussion, explore ASK A VET™. Breathing distress needs immediate veterinary care.