Topic Overview

What is a heart murmur?

A heart murmur is an extra sound that the blood makes as it flows through the heart. Your doctor uses a stethoscope to listen to your heartbeat. When you have a heart murmur, your doctor can hear an extra whooshing or swishing noise along with your heartbeat.

It can be scary to learn that you or your child has a heart murmur. But heart murmurs are very common, especially in children, and are usually harmless. These normal murmurs are called "innocent" heart murmurs. There is nothing wrong with your heart when you have an innocent murmur. Up to half of all children have innocent murmurs.¹ They usually go away as children grow.

Adults can have innocent murmurs too. They can happen when your blood flows harder and faster than usual—during pregnancy, for example, or a temporary illness, such as a fever. They usually go away on their own. Innocent murmurs are often found in adults over 50 years of age.¹

Sometimes, though, a heart murmur is a sign of a serious heart problem. This is called an abnormal heart murmur.

What causes an abnormal heart murmur?

Abnormal murmurs are signs of a heart problem. In children, abnormal heart murmurs are usually caused by problems they are born with, such as a heart valve that doesn't work right or a hole in the wall between two heart chambers.

In adults, abnormal murmurs are most often caused by damaged heart valves. Heart valves operate like one-way gates, helping blood flow in one direction between heart chambers as well as into and out of the heart. See a picture of blood flow through a normal heart.

When disease or an infection damages a heart valve, it can cause scarring and can affect how well the valve works. The valve may not be able to close properly, so blood can leak through. Or the valve may become too narrow or stiff to let enough blood through. When a damaged heart valve cannot close properly, the problem is called regurgitation. When the valve can't let enough blood through, the problem is called stenosis.

Heart valves can be damaged by heart disease or by infections like rheumatic fever or endocarditis. The normal wear and tear that comes with aging can also cause some damage.

Some heart murmurs are caused by a thicker than normal heart. When the heart muscle grows too large, it can get in the way of normal blood flow and cause a murmur.