Heart murmurs are common physical examination findings in pets.  A heart murmur is an abnormal sound that is heard when listening to the heart with a stethoscope.  A murmur can have many different causes, and is actually a clinical sign, not a final diagnosis.

Heart murmurs occur because of a disturbance in the blood flow through the heart, also known as turbulence.  When a normal heart is listened to with a stethoscope, two distinct, repeated sounds are heard.  These are frequently described as “Lub” and “Dub.”  A murmur is an extra sound that causes a variation from the normal “Lub-Dub.” For example, murmurs may cause sounds such as “Lub-whoosh-Dub.”

Turbulent blood flow may have many different causes.  To understand these possible causes, one must be familiar with the basic anatomy of the heart. 

The heart has four chambers: a left and right atrium and a left and right ventricle.  Blood from the body enters the heart through the right atrium.  It then passes into the right ventricle, and is pumped into the pulmonary artery, then to the lungs, where it picks up oxygen.  Oxygenated blood then enters the left atrium, passes into the left ventricle, and is pumped into the aorta, where it delivers oxygen to the body.

Each of the chambers of the heart is separated from other chambers and from major vessels by valves. These valves keep blood flowing in the correct direction.  If the valves do not function properly, blood flow can be disturbed.  “Leaky” mitral valves are one of the most common causes of heart murmurs in dogs.

Turbulence can also develop because of a hole in the wall that separates the chambers of the heart, because of an abnormal connection between vessels near the heart, or because of an abnormally narrow chamber or vessel.  Sometimes, a heart murmur can be heard when a pet becomes excited, and the rate and strength of the heart’s contractions increase.  Anemia, which causes the blood to be too thin, can cause a murmur.

A heart murmur itself cannot be treated.  Treatment instead is aimed at addressing the underlying cause of the murmur.

The severity, location, and particular sound of the murmur can sometimes provide enough information for your veterinarian to determine its underlying cause.  Often, however, additional diagnostic tests are necessary.  Such tests include chest x-rays and an ultrasound of the heart (echocardiogram).  A blood test is also available that helps to determine whether the heart is undergoing significant strain.

Some conditions that cause heart murmurs require treatment to keep them from progressing to clinical disease.  Other murmurs are “benign,” meaning that their underlying cause does not require treatment.

If your veterinarian discovers that your pet has a heart murmur, it is important to realize that the murmur is an alert that the heart may have a problem.  Your veterinarian will discuss the next steps that are best for your individual pet.

Dr. Kelly Sulik owns and operates Animobile Mobile Veterinary Services in Tryon, N.C. She can be reached at animobiledvm@gmail.com.