Heart Murmurs in Dogs and Cats

Your veterinarian told you that your pet has a heart murmur, but what does that mean?

A heart murmur is an additional noise heard due to the abnormal flow of blood through the heart’s valves or chambers. This additional noise is then graded on a scale of 1 to 6 based on how loud the heart murmur is. A 1 means the softest and hardest to hear, and a 6 means the loudest.

How loud the heart murmur is does not necessarily correlate to the severity of heart disease. If your pet has a heart murmur, it is not an immediate cause for panic, but rather lets your veterinarian know that more investigation should be done to try and find the cause.

What Causes a Heart Murmur?

There are many causes of heart murmurs. Some heart murmurs are considered “innocent,” also termed “physiologic.” Other heart murmurs are a result of a disease, and these are known as “pathologic.” Pathologic heart murmurs can be caused by a structural problem with the heart or can be caused by disease not related to the heart itself, called functional heart murmurs.

Innocent Heart Murmurs

An innocent heart murmur means there is no heart disease that explains the presence of the heart murmur. In dogs, these murmurs occur most often in puppies. They can occur in cats of any age.

These murmurs are usually very soft. In puppies and kittens, these murmurs usually appear around 6 to 8 weeks of age and should go away on their own by the age of 4 to 5 months. In adult cats, stress may cause an innocent heart murmur.

Structural Heart Disease

An abnormal defect or structure that disrupts the normal flow of blood leads to structural heart disease. Examples of these include valve disease that causes the valves between the chambers of the heart to not close or open properly, a hole in the heart that causes two chambers or two arteries to be connected when they shouldn’t be, and narrowing or widening of the blood vessels.

Functional Heart Murmurs

Heart murmurs can also be caused by disease outside of the heart, or extra-cardiac disease. There are many causes of functional heart murmurs, including anemia (low levels of red blood cells), fever, pregnancy, infection, obesity, being significantly underweight, and hypoproteinemia (low protein levels in the blood).

Signs, Diagnostics, and Treatment

In some cases, your pet may not be experiencing any signs of having a heart murmur. In others, you may have noticed signs of poor appetite, exercise intolerance, trouble breathing or fast breathing when resting or sleeping, collapse or fainting, weight loss, coughing, pale gums, and weakness.

If your pet is found to have a heart murmur, your veterinarian will discuss additional testing that may be beneficial in finding the cause of the heart murmur and to determine the severity of the condition causing the murmur. Diagnostics that may be suggested include bloodwork, chest X-rays, and blood pressure testing.

Your veterinarian will likely suggest referral to a veterinary cardiologist or an imaging center for an echocardiogram. An echocardiogram is an ultrasound of the heart to get an idea of what the heart looks like and how it is functioning in real time. More specifically, an echocardiogram will provide information about the shape, size, and function of the heart’s four chambers, valves, and other surrounding structures.

Together, these diagnostics will provide your pet’s veterinarian with the information needed to determine what treatment and medication, if needed, will be necessary to help your pet live a longer, happy life.

By Dr. Jeanette Barragan

Illustration from photo by Gajus