Issue Description 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
In some breeds, abnormal development (dysplasia)
of the valve has been identified in the embryo.
Causes 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.
Symptoms Over time 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
Diagnosis 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
Treatment 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.
Breeds Most Affected 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.
small breeds are most often affected. Some studies show a greater
incidence in males than in females.