An enlarged heart in a cat also is known as congestive heart failure. There can be many underlying causes for an enlarged heart, such as valve defects, tumors, heartworms, hyperthyroidism or heart beat abnormalities. If there is an underlying cause that can be cured, then curing the underlying cause can reverse the condition. Unfortunately, most congestive heart failure can only be controlled to extend the life of the cat.
An enlarged heart occurs when the heart can't keep up with the body's circulatory demands. The most common type of heart disease that enlarges the heart of a cat is dilated cardiomyopathy or dilative cardiomyopathy. In this disease, the walls of the heart weaken and thin out and the walls become rounded. The direct cause for this is not known, but genetics is suspected to play a part as well as a lack of antioxidants. A deficiency of Taurine, an amino acid, was a common cause before cat foods began supplementing their food with it. A viral infection earlier in the cat's life also may have weakened the heart.
Most cats will show few symptoms from an enlarged heart until it is in an advanced stage. Some symptoms may include difficulty breathing, much like with asthma; weight loss; listlessness; loss of appetite; weakness; or intolerance to exercise. Coughing is a common symptom for humans and dogs, but it is rare with cats. A heart murmur is an unusual sound or pattern in the heartbeat. This is a symptom of an enlarged heart and can be detected by a veterinarian on a routine physical exam.
Listening for a heart murmur is the first way a vet will check for an enlarged heart. Other tests include X-rays under anesthesia to look for the enlarged heart, which will confirm the enlarged heart but may not confirm the type of enlarged heart and the treatment needed. Other tests could include an electrocardiogram, which traces the electrical activity of the heart; an echocardiogram, which uses sound waves to get a picture of the heart as it beats and to check for fluid in the chest cavity; and a blood test.
If there isn't an underlying cause for the enlarged heart that can be treated, then the treatment usually involves drugs that can control the symptoms. Diuretics will flush out the excess fluid in the lungs and chest cavity. A vasodilator will dilate blood vessels to lower blood pressure so the heart won't have to work as hard. Digitalis can strengthen the heart muscles and fix some kinds of irregular heartbeats. ACE inhibitors also improve the function of the heart. Because of the risk of blood clots, low dosages of aspirin are used to thin the cat's blood. Large cats should be placed on a diet to reduce the workload on the heart.
Unless there is an underlying cause that can be cured, cats with enlarged hearts will slowly worsen, even with treatment. The cat's life expectancy will depend on how soon the condition is caught and the general health of the cat. If it is caught early enough, cats can live symptom-free for years.