Mitral Valve Disease in Small Dogs: From Heart Murmur to Treatment

Myxomatous mitral valve disease is a common heart condition in older small dogs. The mitral valve becomes thickened and no longer closes tightly, allowing blood to leak backward each time the heart contracts. Many dogs live for years with a murmur before they ever develop heart failure.

A heart murmur is not the same as heart failure

A veterinarian may detect a murmur during a routine examination even when a dog appears completely normal. The next question is not simply “Does my dog have a murmur?” but “Has the heart enlarged, and is there evidence that treatment is needed yet?”

How the disease is assessed

Depending on the dog, evaluation may include chest X-rays, echocardiography, blood pressure measurement and blood tests. Echocardiography shows valve structure and heart-chamber size, while X-rays can help assess heart enlargement and the lungs.

Why staging matters

Veterinary cardiology uses stages to separate dogs with only a risk or murmur from dogs with enlargement and dogs that have developed congestive heart failure. Medication recommendations differ by stage, which is why giving a heart drug simply because a murmur exists is not appropriate.

Treatment when heart failure develops

Dogs with congestive heart failure generally need a combination of medications to reduce fluid accumulation and improve heart function. The exact plan is individualized and requires follow-up because kidney values, electrolytes, breathing and clinical response can change.

What you can monitor at home

• Sleeping respiratory rate, if your veterinarian asks you to track it
• New coughing or faster breathing
• Exercise tolerance
• Appetite and body weight
• Fainting or collapse episodes

Nutrition and activity

Keeping a healthy body condition is useful. Do not start extreme sodium restriction, supplements or “cardiac diets” solely because of breed or a soft murmur; nutritional changes should match the stage of disease and the dog’s other health needs.

Emergency signs

Labored breathing, rapid breathing at rest that is clearly abnormal for your dog, blue-gray gums, collapse or inability to lie comfortably requires urgent veterinary attention.

If your dog is older, our senior nighttime restlessness guide and Small Dog Health Guide may also be useful.

Learn the dog’s normal sleeping breathing rate

For dogs with diagnosed mitral valve disease, veterinarians may recommend monitoring breathing while the dog is fully asleep. The useful part is the trend: a persistent increase above that dog’s usual pattern can be more meaningful than a single isolated count. Ask your veterinarian what range and action threshold they want you to use for your dog.

Do not wait for a dramatic cough to report change

Reduced stamina, faster breathing at rest, difficulty settling, fainting or a change in appetite can all matter. Heart disease progresses at different rates, so scheduled rechecks are important even when a dog seems comfortable. Emergency breathing difficulty or collapse requires immediate veterinary assessment.

Explore the complete guide: For health monitoring and daily comfort as small dogs age, see our Senior Small Dog Care Guide.