Heart murmurs are found in both young and older dogs. Usually heart murmurs in young dogs are congenital whereas heart murmurs in older dogs are likely to have heart valve diseases. Heart murmurs are common occurrences in dogs.
Heart murmurs describe an abnormality in the way the heartbeat sounds when listened to with a stethoscope. Unlike the sharp, short beat of a normal heart, the murmur is a softer and longer noise. It is caused by abnormal blood flow through the heart and it indicates exactly that.
In Evaluation of Cough in Dogs with Heart Murmurs, Clarke Atkins discusses in detail types of coughing and how to pinpoint when the coughing is related to a heart murmur."Overall, the most useful tool is the thoracic radiograph." Heart murmurs may be classified as (1) innocent, (2) functional, or (3) pathologic.
Each side of the heart has a one-way valve to keep blood from going backward from the ventricles to the atria. The valve between the left atrium and left ventricle is called the mitral valve. Because of the high pressure created when the left ventricle contracts, the mitral valve will begin to leak or “wear out” in many dogs. This is known as mitral valve insufficiency and is often associated with a heart murmur.
The earliest sign of a leaking mitral valve is a heart murmur. This is produced when some of the blood goes backward through the leaking valve into the left atrium. Many dogs develop a murmur from the mitral valve as early as six years of age. This problem is especially common in small breeds of dogs. A heart murmur does not mean that heart failure is imminent. But as time goes on, the leak becomes more severe and more and more blood flows backwards. This results in reduced pumping efficiency and, eventually, congestive heart failure. From the time a murmur develops, it may be a few months to several years until heart failure occurs.
When it is possible, economically, for the owner of a puppy with a heart murmur to have a cardiac ultrasound exam done, I think that is the best course of action. It is unquestionable that many murmurs that are present congenitally will never cause any problem during a dog's lifetime. However, it is also definitely true that some do.
Ultrasound exam is the best way to evaluate heart murmurs because it gives a good idea of how much of the blood flow in the heart is being misdirected and also identifies readily where the defect is that is allowing the blood flow to produce a murmur. When it isn't possible for a pet owner to comfortably pay for cardiac ultrasound exam, we do our best to evaluate the overall situation and advise the owner based on clinical signs present.
If a puppy is gaining weight normally, is active and doesn't tire readily, has a normal red blood cell count adjusted for his or her age and isn't showing any other signs of heart disease, we advise just waiting to see what happens. If there are definite clinical signs of heart disease, in addition to the murmur, we push much more strongly for advanced testing. Since cardiac ultrasound exam is by far the most effective method of evaluating heart murmurs, I'd skip things like ECGs to get the ultrasound exam, if a choice has to be made between tests.