Glossary
Mitral valve disease
A slow wearing of the heart's mitral valve that lets blood leak backward, the most common heart disease in older small-breed dogs.
Also called: MVD, degenerative mitral valve disease, DMVD, heart murmur, leaky heart valve
The mitral valve separates the upper and lower chambers on the left side of the heart. In mitral valve disease the valve thickens and no longer closes tightly, so some blood leaks backward and a vet hears a murmur through the stethoscope.
It is the most common heart disease in dogs, especially older small and medium breeds. The Cavalier King Charles Spaniel is well known for developing it early, often in middle age.
Many dogs live for years with a murmur and no symptoms. In some, the disease advances to heart failure, with coughing, fast or labored breathing at rest, and tiring easily. A murmur is a finding, not a diagnosis, so a veterinarian may recommend a chest X-ray or heart ultrasound to grade it. A dog with breathing trouble needs prompt care.
Last reviewed November 8, 2026