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Dear Dr. Jorden: My cocker spaniel is now 9 years old and has a heart murmur.

My vet said it has to do with the heart valve and we have to watch for heart failure. What kind of things can I expect?

The most common type of heart problem in older dogs is usually a failure of one or more of the heart valves.

Inside the heart there are thin, flexible flaps that separate the chambers of the heart. There are also valves in the aorta, which is the main artery leaving the heart.

Their purpose is to flap open when the heart muscle contracts to move the blood and then to close against each other as the heart relaxes and expands. There are two valves opposite of each other at each location.

When the valves work properly, the blood is easily pushed forward. Without valves, the blood would not circulate through the body but would just move back and forth.

When the valves shut to stop the blood from moving back, they seal the opening so that no blood is allowed back through. If, for some reason, the valves are not meeting correctly or are not sealing off the opening, some of the blood squirts back through the opening with each beat of the heart.

This is what makes a distinct sound that can be heard with the stethoscope by your veterinarian. It is a lot like stepping on a garden hose so that it closes down on the water flow. You can hear the water in the hose at the narrow spot.

Valves wear out with age and malfunction. Sometimes bacteria will grow on the valves and cause them to be misshapen. Heartworms living in the heart will cause valves to malfunction. The heartworms can actually be physically in the way of the valve.

When the valves are not working completely correctly, the heart has to work harder to get the blood to flow properly. As the heart works harder, like any other muscle, it starts to get thicker and larger because of the excessive work load it carries.

As the valves and heart muscle begin to fail, there is often blood and fluid that backs up into the lungs. Fluid accumulation in the lungs will cause your dog to start coughing.

At first, it will be a minor cough that occurs when he exercises or exerts himself. As the heart fails, it will become a constant cough.

Treatment for many heart problems is directed at controlling the amount of fluid that is building up in the lungs. Diuretics are used to drain the water off the lungs.

Fluid may also build up in the rest of the body. Diuretics help with that as well. As the heart fails further, the diuretics begin to stop working as well because the circulation to the kidneys where the diuretics have their effect is compromised and the fluid can no longer be removed.

The good news is that many dogs do not progress very rapidly. I have treated, successfully, many dogs for years without the heart changing very much.

There are times, when it does progress rapidly with treatment failing in a matter of months. The best thing to do is to follow through with all your veterinarian's recommendation and have your pet examined frequently so the medical plan can be adjusted to his needs before there is a crisis.

Have questions about pets? Write to: PetVet; c/o The Billings Gazette; P.O. Box 36300; Billings, Mont. 59107-6300. Questions of general interest may become topics of future columns.