A heart murmur is an abnormal heart sound that is heard during a heartbeat. A murmur indicates that there is a problem, but is not specific for any one condition. Most heart murmurs in dogs are found when a veterinarian listens to a dog’s heart during a routine physical examination.
In healthy hearts, blood flows through the heart and blood vessels in one direction. Valves between the heart chambers prevent backflow of blood. When there is an abnormality affecting the heart muscle, heart valves, or outflow tracts (blood vessels leaving the heart), blood can flow backwards through the valves, causing turbulence resulting in the sound of a murmur.
Most conditions that cause a heart murmur have no symptoms in the early stages, but once the condition progresses dogs typically develop some combination of the following:
- decreased appetite
- weight loss
- inability to exercise normally
- difficulty breathing
Most dogs with murmurs have some type of heart disease. Possibilities include leaky valves, weakened heart muscle, infections of the heart valves, cancer of the heart, or birth defects affecting the heart. Systemic diseases may cause heart murmurs as well. Anemia, severe infections, fever, and emaciation are examples of non-cardiac diseases that can result in a murmur.
Some murmurs, especially those affecting puppies, are called “benign,” meaning that no physical abnormality can be found and the murmur often goes away as the dog matures. “Physiologic” murmurs are those that are typically seen in adult dogs that are extremely excited or stressed. This type of murmur usually resolves when the dog is calm.
A dog’s signalment (age, sex, and breed), plus a careful physical examination that includes listening to the heart with a stethoscope may provide a good idea as to the underlying cause of the murmur. Chest x-rays and an echocardiogram (ultrasound of the heart) will usually definitively diagnose any underlying heart conditions that are responsible for the murmur. Additional testing like blood work, blood pressure testing, and an electrocardiogram (ECG) may also be needed to fully assess the dog’s condition and plan appropriate treatment.
The treatment and prognosis for dogs with a heart murmur varies depending on the underlying condition. Benign or physiologic murmurs carry a good prognosis and should simply be monitored. Diseases of the heart are often slowly progressive with no noticeable symptoms for months or years. Once symptoms of advanced heart disease and/or congestive heart failure develop, treatment can help to reduce their severity for a period of time.
Regular examinations (once to twice yearly) are important for keeping dogs as healthy as possible. Early recognition of problems typically results in better outcomes. Whenever new symptoms develop, schedule an examination with a veterinarian as soon as possible.