Heart Murmurs

It is not uncommon for a veterinarian to discover a heart murmur in an otherwise healthy 8 year or older canine patient. The news of the murmur for the pet owner often comes as a surprise, and leads to the question, what should be done?

The most common type of murmur in an aging patient is called MMVD, which stands for myxomatosis mitral valve disease. This is primarily a wear and tear disease of the “three leafed” valve between the left atrium and left ventricle. Essentially the valve leaflets become thickened and irregular over time and no longer provide a tight seal when closing. The absence of a tight seal leads to back flow of blood through the valve, which creates the turbulence that we hear with the stethoscope, and is called a murmur.

This type of mitral valve disease often eventually leads to congestive heart failure in the patient. However MMVD is characterized by a long preclinical phase. This means a long time between when the murmur is first noticed and the onset of clinical signs. Until recently no therapies have been proven to prolong this time before the onset of congestive heart failure (CHF).

The question for the doctor was always, “is there a benefit to the patient, to begin a heart medication prior to any clinical signs of CHF?” In other words was there anything that could be done about this murmur?

A recent study demonstrated the benefit of pimobendan (a heart medication), in significantly prolonging the time of onset of CHF or cardiac related death in dogs with MMVD and heart enlargement.

In this study it was determined that dogs with MMVD and heart enlargement; proven by radiology and echocardiogram, would benefit from starting the drug pimobendan early on, prior to any clinical symptoms.

This information is a big leap forward for the canine patient with a heart murmur. Starting medication early on will delay the onset of CHF and cardiac related deaths. In the middle aged patients with MMVD and proven heart enlargement there is now a clear recommendation from the veterinary profession.

In answer to the earlier question “what can be done for a non-clinical patient with an established heart murmur?”

Chronic oral therapy with pimobendan should be initiated every 12 hours in these patients. The medication is safe and well tolerated by dogs and once started, long term prognosis is substantially improved. In fact the study showed the preclinical time period was doubled!

Pimobendan is not a new drug but rather has been used to treat patients in CHF, it is the idea of starting the medication early on that is new and quite beneficial. This is another step forward for pets and veterinary medicine.


Dr. Alan Main is the owner of West Suburban Veterinary Practice and his dedicated team have been providing services to the West Suburban Humane Society for over 10 years.

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