What Is Mitral Valve Disease?
Mitral valve disease (often called myxomatous mitral valve disease, or MMVD) is the most common heart disease in older small-breed dogs. The mitral valve sits between the left atrium and left ventricle. With age-related degeneration, the valve leaflets thicken and fail to seal tightly, so blood leaks backward (mitral regurgitation) when the ventricle contracts.
Owners usually first hear about it after a vet finds a heart murmur on a routine exam. Cavalier King Charles Spaniels, Dachshunds, Chihuahuas, Pomeranians, and many other small breeds are over-represented, but any dog can develop it. Cats can have mitral valve disease too, though hypertrophic cardiomyopathy is the more common feline heart story in US clinics.
Why it matters
A soft murmur can progress over months to years into cough, breathing trouble, or congestive heart failure. Early staging with X-rays and echocardiography guides when to start heart medications — waiting until a dog is in crisis is harder on everyone.
Signs Owners Notice
- A heart murmur detected at a wellness visit (often before any home signs)
- Cough, especially at night or after excitement, as the enlarged atrium presses on airways or fluid builds in the lungs
- Faster or harder breathing at rest; reluctance to exercise
- Restlessness at night, gagging, or “trying to clear the throat”
- In advanced disease: pale or bluish gums, collapse, or open-mouth breathing — emergency signs
Many dogs live comfortably for a long time with mild disease. Change in breathing rate at rest is one of the most useful home monitoring tools your vet may teach you.
Diagnosis and Treatment
Diagnosis combines auscultation (listening), chest X-rays, blood pressure, bloodwork, and ideally echocardiography (heart ultrasound) to stage severity (often discussed with ACVIM stages B1, B2, C, and D). Staging decides whether to watch, start pimobendan or other cardiac drugs, add diuretics for fluid, or refer to a veterinary cardiologist.
Treatment is individualized:
- Stage B1 (murmur, no significant enlargement): usually monitoring.
- Stage B2 (enlargement without failure): many dogs benefit from starting pimobendan based on landmark trial data — your vet explains the evidence for your dog.
- Congestive heart failure (stages C/D): diuretics, diet sodium guidance, activity plans, and frequent rechecks.
There is no simple “pill that cures” degenerative valve disease; the goal is quality of life and delayed progression. Never start or stop heart meds from internet protocols.
Practical Tips for US Pet Owners
- Ask your vet to show you how to count resting respiratory rate at home (often under ~30 breaths/minute at true rest — confirm your dog’s target).
- Keep a log of cough, appetite, and energy; bring it to cardiology or GP rechecks.
- Maintain healthy weight — extra pounds make breathing and heart work harder.
- Use heartworm prevention as directed; concurrent heartworm disease complicates murmurs.
- If a cough starts suddenly with hard breathing, go to emergency care the same day.
When to see a vet
Schedule promptly for a new or changing murmur, nighttime cough, or rising resting respiratory rate. Seek emergency care for open-mouth breathing, blue/pale gums, collapse, or refusal to lie down because breathing feels easier sitting up.
Key Takeaways
- Mitral valve disease is the leading heart disease of aging small-breed dogs and often starts as a murmur.
- Staging with imaging decides monitoring versus medication for enlargement or heart failure.
- Home breathing-rate checks and early rechecks protect quality of life better than waiting for a crisis.
FAQ
Is every heart murmur mitral valve disease?
No. Murmurs have many causes. Imaging confirms which valve is leaking and how severe the changes are.
Can diet reverse mitral valve disease?
No diet reverses degenerative valve changes. Sodium guidance and weight control support dogs in or near heart failure — follow your veterinarian’s plan.
Do cats get the same disease dogs do?
Cats can have mitral valve disease, but hypertrophic cardiomyopathy is more often discussed in feline cardiology visits in the US.