related terms: mitral valve disorder, mitral valve malformation, mitral dysplasia, mitral systolic murmur

What is mitral valve disease?

The heart consists of 4 chambers - 2 atria and 2 ventricles. The atrioventricular (AV) valves ensure that the blood flows from the atria to the ventricles when the heart beats. A defect in the mitral valve (the left atrioventricular valve) causes backflow of blood into the left atrium, or mitral regurgitation. Less commonly, a narrowing or stenosis of the valve can be identified. Because of the leaky valve, the heart is less efficient at pumping blood to the body. Mitral valve insufficiency is the most common acquired cardiac disease in older dogs, affecting over one third of dogs greater than 10 years of age. In some breeds however, mitral insufficiency develops at a much younger age, due to an inherited predisposition for this disorder.

In some breeds, abnormal development (dysplasia) of the valve has been identified in the embryo.

How is mitral valve disease inherited?

Although the pattern of inheritance has not been identified, it is agreed that there is a genetic basis for the early development of mitral valve disease.

What breeds are affected by mitral valve disease?

There is a relatively high incidence of early development of mitral valve disease in the cavalier King Charles spaniel, Cairn terrier, miniature poodle, and bull terrier (particularly in the United Kingdom).

It is also seen, not as commonly, in the miniature pinscher, toy and standard poodle, Boston terrier, whippet, chihuahua, Pekingese, dachshund, beagle, papillon, great Dane, and German shepherd.

In general, small breeds are most often affected. Some studies show a greater incidence in males than in females.

For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a general consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.

What does mitral valve disease mean to your dog & you?

Dogs often compensate well for years, despite mitral regurgitation (backflow). You can help by maintaining your dog at a healthy weight,  and ensuring regular exercise and a good diet.

Over time however, changes will occur in your dog's heart because of the increased work to make up for the insufficient, or leaky, mitral valve.  Early signs that the heart is no longer able to compensate for mitral valve disease may include a reduced tolerance for exercise, difficulties in breathing, or a cough at night or at rest. All of these occur because of a build-up of fluid in the lungs. Other signs of a gradually failing heart include fainting, weakness, or collapse, which may be due to an abnormal heart rhythm (cardiac arrhythmia).

How is mitral valve disease diagnosed?

Your veterinarian may detect a heart murmur before your dog is showing any signs associated with mitral valve disease. Further investigation by radiographs and electrocardiogram may reveal some of the changes that occur in the heart over time, as it works harder to compensate for the insufficiency of the mitral valve. These changes may include enlargement of the left side of the heart, enlargement of blood vessels in the lungs, and cardiac arrhythmias.


MURMUR: soft to loud, harsh, regurgitant, holosystolic - loudest at left apex (5th to 6th intercostal space) over the mitral valve area.
ELECTROCARDIOGRAM: commonly see left atrial enlargement pattern (increased P wave duration) with or without left ventricular enlargement (depends on severity). Atrial arrhythmias, especially atrial fibrillation, are common.
RADIOGRAPHS: moderate to marked left atrial enlargement with or without left ventricular enlargement. Pulmonary veins are often enlarged.
ECHOCARDIOGRAPHY: may see abnormal location, shape, motion or attachment of the valve apparatus. Doppler assessment will show an abnormal flow (regurgitant jet or valvular stenosis or both).

How is mitral valve dysplasia treated?

There is no cure for mitral valve disease but your veterinarian can recommend medical therapy to ease life for your dog. Depending on the stage of heart disease, this may include a special sodium-restricted diet, exercise restriction, diuretics, and medication to support the failing heart.

One obstacle to controlling mitral valve disease is that clinical signs associated with the disorder are generally not evident until after a dog has reached breeding age. However a heart murmur can often be detected long before the onset of clinical signs. In the United Kingdom and in Sweden, the cavalier King Charles spaniel clubs have instituted certification programmes whereby dogs are examined annually for a cardiac murmur by veterinarians. One copy of the resulting certificate is retained by the owner/breeder, and one forwarded to the breed club. Breeders are encouraged to select mature rather than young dogs for breeding, that have been certified free of murmurs. Swedish law prohibits the use for breeding of dogs with any congenital heart disease.

Similar certification/central registration programmes could be established in other countries.



Patterson, D.F.  1996.  The genetics of canine congenital heart disease.  ACVIM - Proceedings of the 14th Annual Veterinary Medical Forum: 225-226.  This reference has good information for breeders and veterinarians regarding screening and genetic counselling for congenital heart defects.

Copyright © 1998 Canine Inherited Disorders Database. All rights reserved.
Revised: July 05, 2004.

This database is funded jointly by the Animal Welfare Unit at the Atlantic Veterinary College, University of Prince Edward Island, and the Canadian Veterinary Medical Association.