Humans don't have a monopoly on heart disease - our furry friends also are susceptible to a wide range of cardiovascular conditions. Smaller breed dogs, in particular, are more likely to develop heart disease, including heart "murmurs."

Heart murmurs occur when the animal's heart function has deteriorated, creating an abnormal blood flow within the heart's chambers. The condition may be congenital, meaning the animal was born with the problem, or else it can develop as the result of disease and aging. Some conditions aren't very serious; others will progress rapidly, causing congestive heart failure and death.

Like humans, a dog's heart has four chambers and is divided into left and right sides. The two chambers on top of the heart are the left and right atria, and the bottom two chambers are the left and right ventricles. Each side of the heart also contains a one-way valve, designed to prevent blood from going backward from the ventricles to the atria. The valve between the left atrium and left ventricle is the mitral valve, a key structure in regulating blood flow through the heart.

Aging, disease, and birth defects can cause the mitral valve to wear out. When this occurs, blood begins to leak back into the ventricles, a condition known as mitral valve insufficiency. It's a condition that produces the distinctive sounds known as a heart murmur.

A chronic cough, labored breathing, and limited ability to exercise are key symptoms that your dog may have a heart problem. In severe cases, the animal may faint, or exhibit a bluish tinge around the gums and tongue. Many dogs develop the condition as early as age six, especially in smaller breeds, such as miniature poodles and dachshunds. Diagnosis and treatment by a veterinarian is critical, since the presence of a heart murmur can lead to congestive heart failure in as little as a few months. In many dogs, however, treatment can provide them with additional months or years of good-quality life.

Diagnosis of a heart murmur is done by listening to the dog's chest with a stethoscope to identify any abnormal heart rhythms. Blood and urine tests also can detect the presence of heart disease. Chest x-rays allow more detailed examination of the lungs, as well as the size and shape of the heart. An electrocardiogram evaluates the heart's electrical activity, while an ultrasound (echocardiogram) gives a highly accurate view of each of the heart's chamber sizes and the thickness of the heart walls. From these, the heart's contractions can be measured to determine how well it's able to pump blood through the dog's body.

Treatment for heart murmurs normally starts by placing the dog on a low-sodium diet and using diuretic medications to eliminate retained salt and water. Other drugs are prescribed to dilate the arteries and veins (thereby decreasing stress on the heart), and digoxin (digitalis) is also given to make the heart beat slower and stronger. Once diagnosed, most dogs survive anywhere from six months to several years, with treated dogs obviously living longer than untreated ones.