Q My cat has recently been diagnosed with a heart murmur. Is this something to worry about and should I have it checked out further?

A: A heart murmur may be congenital or acquired with age. Congenital means the problem causing the murmur was present at birth. Since your cat was only recently diagnosed with a murmur, it is probably acquired, meaning the heart was normal at birth but something has changed over time.

There are two primary reasons for these murmurs that occur later in life.

One is a narrowing in the area where blood leaves the heart and goes into the aorta. The narrowed opening causes the blood to flow out of the heart at a higher velocity, creating a swishing sound. This is the same as when you narrow the opening on your garden hose and the water shoots out further with a louder sound.

The second cause is a leak in a heart valve. There are four one-way valves in the heart. These insure blood moves forward and leaves the heart and does not flow backwards. If the valves no longer close properly, then blood may leak backwards at a high velocity, creating a swoosh.

The most common form of heart disease we see in cats is called hypertrophic cardiomyopathy, HCM. This term means thickening (hypertrophy) of the heart muscle. This thickening causes several problems. First, it will alter the shape of the heart, which often results in the valves no longer closing properly resulting in a leak.

The second problem is the hypertrophied muscle does not relax enough. There are two phases to a heartbeat, the contraction to force blood forward, systole, and the relaxation to allow blood to fill the heart, diastole. When blood cannot get into the heart, it starts to back up in the vessels and eventually may lead to heart failure.

The third problem is the thickened heart muscle may narrow the opening that blood flows through into the aorta. This may make the hypertrophy worse as the heart tries to strengthen to force blood out of the narrowed opening.

The eventual outcome is heart failure. This manifests as trouble breathing from fluid accumulating between the ribs and lungs, causing the lungs to collapse. Pulmonary edema also may develop where fluid actually accumulates in the lungs themselves.

This fluid makes it hard for oxygen to go from the air into the blood. Some cats will actually develop both types of heart failure simultaneously. Once this starts, it is fatal without intervention.

Another complication of heart disease in cats is the development of blood clots. It is not completely understood why these clots form and not all cats with heart disease will develop them. When they do occur, however, it is often life threatening. These clots form in the left atrium and leave the heart out through the aorta. They travel until they reach a vessel that is too small for them to pass. This obstructs blood flow to that area, damaging or even killing the region. They can go anywhere, but the most common spot is where the aorta branches to carry blood to the back legs. A clot here will cause sudden, painful paralysis. If complete, this can be fatal.

The frustrating thing is that there are no medications that will slow the progression to heart failure. However, cats can have severe hypertrophy and not develop heart failure for years.

Aspirin and Plavix are used to decrease the likelihood of clot formation. No great study exists to prove they work, though.

Most of the time there is hereditary predisposition to the development of the disease, so there is nothing we can specifically treat to reverse these changes. But there are two problems every cat with HCM should be tested for: hyperthyroidism and hypertension.

If the heart changes are secondary to these problems, they may be reversible. So if your cat is diagnosed with a heart murmur, make sure blood pressure and thyroid hormone level are measured.

Male, large-breed cats such as Maine Coons and ragdolls appear to be at greatest risk, but any cat can develop this disease.

Once in heart failure, there are therapies that can be given to reverse the symptoms. The pleural fluid can be drawn off with a needle and syringe, allowing the lungs to expand and offering immediate relief. Diuretics, such as Lasix, can be given to reverse the pulmonary edema. Oxygen therapy is sometimes needed to support the cat until the therapy starts to work.

Even after going into heart failure, some cats can be maintained on medications for months to years.

At home, the signs to watch for impending heart failure are a rapid heart rate and a rapid respiratory rate at rest.

Thoracic X-rays and heart ultrasound are the best tools a veterinarian can use to look at your cats heart.

To finally answer your question, yes, it is important to have your cat's heart assessed further.

If he has hypertension or hyperthyroidism, you may be able to intervene and reverse the changes. If he has heart disease, you can know what type and if heart failure or a blood clot is something you should be worrying about.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to petdocs@postandcourier.com or veterinaryspecialtycare.com.