A heart murmur in a puppy or a kitten may or may not be a serious problem. A murmur is an abnormal sound that is heard when ausculting (listening) to the heart with a stethoscope. Murmurs are due to atypical blood flow in the heart or the surrounding vessels, but they do not necessarily confirm the presence of heart disease. Typically, the louder the murmur the more concern about the possibility of significant cardiac disease.
Murmurs in puppies and kittens can be placed in two categories: first, murmurs that are a result of actual heart disease, also referred to as pathologic murmurs, and second, murmurs that are present with a normal heart, also referred to as innocent or flow murmurs. Therefore, it is possible to have a mild murmur with a completely normal heart (innocent murmur). The cause of innocent murmurs in both humans and animals is unknown, but the prognosis with an innocent murmur is excellent. Many innocent murmurs will also resolve as the patient ages. Pathologic murmurs are of much more concern. Unfortunately, differentiating between an innocent and a pathologic murmur can be difficult by just listening to the heart during a physical examination. If a murmur is heard, then a special test called an echocardiogram is often necessary to determine if actual heart disease is present.
An echocardiogram is an ultrasound examination of the heart. It is easily tolerated by the patient, and it is the most accurate test for the presence of heart disease. In addition, an echocardiogram is very good at determining the severity of disease. Your veterinarian may need to refer you to a specialist for the echocardiogram.
If your veterinarians notices a heart murmur in your new puppy or kitten you have three options. The first and very difficult option is to return the puppy. The second option is to have an echocardiogram performed to assess whether there is significant heart disease present. It may be helpful to review your sales agreement, because some pet stores and breeders will help you pay for the echocardiogram. The third option is to have the puppy examined again in 1-2 months. As discussed above, some innocent murmurs will resolve over time. If the murmur resolves it is unlikely to be of concern in an otherwise normal animal. The main concern with the third option is the possibility of the puppy having significant heart disease that was not detected early. Whether a murmur is associated with a shortened life span is completely dependent on the presence or absence of heart disease, and the severity of the disease.
Dr. Donald Schrope, DVM, DACVIM (Cardiology)