A murmur is caused by turbulent or fast blood flow within the heart or associated vessels. The turbulence causes a “whooshing” sound, or what is termed a “murmur”, usually heard only with a stethoscope unless it is very loud.

Mild heart murmurs may show no outward signs. Louder murmurs may cause symptoms such as coughing, weakness, exercise intolerance, or collapse.

There are numerous situations that result in a murmur. Some murmurs are benign and are not associated with any structural heart disease. Other murmurs are caused by abnormal blood flow associated with a variety of cardiac conditions, including abnormal heart valves, thyroid disease, and different congenital defects.

Soft, “innocent” murmurs are commonly heard in young puppies and kittens. These murmurs are not associated with any cardiac disease and should disappear by approximately four months of age. Adult animals may have similar murmurs caused by conditions such as stress or fever. A loud murmur in a kitten or puppy is never “innocent” and may indicate a congenital heart defect. Pets with this condition should see a cardiologist for further evaluation. The most common cause of a murmur in older dogs is endocardiosis, or degenerative valve disease. The most common cardiac disease associated with a murmur in adult cats is hypertrophic cardiomyopathy, a primary disease of the cardiac muscle. Older cats may have thyroid disease and treatment for this disease can diminish some murmurs and improve heart function.

Murmurs can be heard during examination with a stethoscope and are classified by the strength of the sound using Roman numerals (Grades I – VI). The side or area of the chest where the murmur is loudest may indicate the source of the problem, but the actual cause of the murmur cannot always be diagnosed without an echocardiogram (an ultrasound of the heart).

Usually no treatment is indicated for mild murmurs. However, lower grade (“innocent”) murmurs should be rechecked at least annually to determine if they are still present and to assess whether they are getting louder or more pronounced, indicating a potential problem. Louder murmurs require cardiac ultrasound examination to determine if abnormal function or a congenital defect is present, and whether medication and/or surgery may be required.

There are no specific requirements for home care.

Mild heart murmurs are usually not a serious concern. Louder murmurs may indicate underlying heart disease.