Heart Murmurs in Pets: What Do They Mean?

The most common reason an animal is referred to a cardiologist is because another veterinarian heard a heart murmur.

What is a heart murmur?

A heart murmur is an extra “whooshing” sound. A heart murmur indicates that blood is moving abnormally within the heart. While heart murmurs are most commonly the result of heart disease, they can also be caused by non-cardiac illnesses. Some murmurs are not associated with any noticeable disease at all. Your primary veterinarian will ask you historical questions and perform a physical exam to determine what the next best steps are, including deciding if your pet should see a cardiologist.

Heart murmurs are usually graded by their loudness using a scale of one to six, with six being the loudest. This grading scale is admittedly somewhat subjective, and the loudness of a heart murmur does not necessarily correlate to the severity of the patient’s disease. Murmurs are also characterized by where they are best heard on the chest as well as when they occur during a single heart beat. Most heart murmurs in dogs and cats are systolic, meaning they occur when the heart is actively pumping blood out.

A heart murmur is not the same thing as an arrhythmia (an abnormal heart rhythm). While animals with heart disease may have both a murmur and an arrhythmia, the two do not necessarily occur together, and different diagnostics are used to investigate each.

What kinds of heart disease cause a heart murmur?

Heart diseases that cause heart murmurs may be acquired (meaning the disease arose as the animal got older) or congenital (meaning the animal was born with a heart disease).

The most common reason for a heart murmur is a problem with one of the valves in the heart. The heart is made up of four chambers and four valves. These valves serve to keep blood flowing in one direction as blood moves through the chambers and out to either the lungs or the body. Valves may be leaky, narrowed, or may move abnormally, all of which can cause a heart murmur.

In dogs, the most common reason for a heart murmur is a leaky valve. The picture is less clear in cats, and many cats do not have an obvious cause for their heart murmur.

Some very young animals may have a heart murmur that goes away as they get older. These “puppy / kitten” murmurs are typically fairly quiet and are usually gone by the time the animal is five or six months of age. Young animals that have loud murmurs, murmurs that are not systolic, or who have a murmur that persists beyond 6 months of age should be seen by a cardiologist.

What testing is done to investigate a heart murmur?

The best test to look for the cause of a heart murmur is an echocardiogram. This is an ultrasound of the heart that allows the cardiologist to look specifically at the heart’s structure and function. Often, a reasonable guess may be made based on the patient’s breed, age, murmur characteristics, and tests such as chest X-rays, though it is rare a specific diagnosis can be made without an echocardiogram.