A heart murmur is an abnormal heart sound that a veterinarian can identify using a stethoscope. Heart murmurs are graded on a scale of 1 to 6 based on the severity of the murmur. A grade 1 is a minor murmur while a grade 6 can be heard even without the stethoscope being pressed directly against the chest. Veterinarians tend to describe heart murmurs in terms of rubbing or vibrating in the chest. Murmurs can be caused by many different underlying conditions and are merely symptoms of a larger problem.
Congestive Heart Failure
It is important to note that heart murmurs themselves are not treated. Because they are symptoms of an underlying condition, the underlying condition itself is treated. As the underlying condition begins to improve, the grade of the murmur might improve, though not always. In the case of heart murmurs caused by congestive heart failure, drugs commonly prescribed include diuretics to remove excess fluids, angiotensen converting enzymes that help to decrease the workload on the heart and digoxin to assist the heart in contracting fully and help to slow heart rate.
Heart murmurs with a congenital origin, meaning that the dog inherited the murmur from an ancestor, might not receive drug therapies as a treatment as most congenital defects are structural in nature. These defects are often corrected through surgery or the implantation of a device used to correct the defect. Dogs that undergo surgery to correct a structural defect to the heart might be prescribed blood thinners to prevent clotting and/or steroids to prevent an immune response to the implanted device.
Chronic Valve Disease
Many heart murmurs, even those as significant as a grade 5, do not require treatment. If an older dog begins to exhibit a heart murmur, drugs will not be prescribed if the murmur is a result of physical changes to the valves of the heart and not to congestive heart failure. This is known as chronic valve disease and involves the thickening of the walls of the valves, which promotes a backflow of blood into the left atria from the left ventricle upon contraction. The same holds true for younger dogs that have congenital heart murmurs in which surgery is not indicated.
Grade 5 heart murmurs that are a result of pericardial effusion or a build-up of fluid in the sac that surrounds the heart can be treated with diuretics to attempt to remove some of the fluid. This is done because the presence of the fluid compresses the heart, making it much more difficult for the heart to perform.
Grade 5 murmurs caused by heartowrm disease are usually cured after the heartworms have been treated unless significant damage to the heart muscle has occurred after a prolonged infection or unusually large worm burden. In these instances, a heart murmur is usually downgraded to a lower classification of severity and ongoing treatment is generally not necessary.