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A heart murmur is an abnormal sound made by turbulent blood flow within the heart. A murmur can be either a normal sound or an indication of a problem.

Most often, the turbulence is normal and is called a benign flow murmur. It happens when blood flows faster through the heart, for example in a person who is anxious, has just finished exercising, has a high fever or has severe anemia. About 10% of adults and 30% of children (most between the ages of 3 and 7) have a harmless murmur produced by a normal heart. This type of murmur is also called an innocent murmur.

A heart murmur may indicate a structural abnormality of a heart valve or heart chamber, or it may be due to an abnormal connection between two parts of the heart. Some abnormalities of the heart that create heart murmurs include:

A heart valve abnormality

The heart has four valves: the aortic, mitral, tricuspid and pulmonary valves. A heart murmur can occur when any one of these valves has a narrowing of the valve opening (stenosis) that interferes with the outflow of blood or a valve leak (regurgitation or insufficiency) that causes a backflow of blood.

Mitral valve prolapse

In this condition, the leaflets of the mitral valve fail to close properly, allowing blood to leak back from the heart’s lower left chamber (the left ventricle) to the upper left chamber (the left atrium).

Congenital heart problems

Congenital means the disorder was present at birth. Congenital heart problems include:

Septal defects

These are also known as holes in the heart. They are abnormal openings in the heart’s septum (the wall between the heart’s left and right sides).

Patent ductus arteriosus

Before birth, the channel between the pulmonary artery and the aorta (called the ductus arteriosus) allows blood to bypass the lungs because the fetus is not breathing. Once a child is born and his or her lungs are functioning, the ductus arteriosus normally closes. Patent ductus arteriosus occurs when blood flow through the ductus arteriosus continues after birth.

Endocarditis

Endocarditis is an inflammation and infection of the heart valves and endocardium, the inner lining of the heart chambers. A heart valve infection can cause a heart murmur by causing blood to leak backwards, or the infected valve can partially obstruct blood flow.

Cardiac myxoma

A cardiac myxoma is a rare, benign (noncancerous) tumor that can grow inside the heart and partially obstruct blood flow.

Asymmetric septal hypertrophy

Asymmetric septal hypertrophy is an abnormal thickening of the heart muscle inside the lower left chamber (left ventricle) of the heart. The thickened muscle makes the outflow passage narrow just below the aortic valve. This condition, also called idiopathic hypertrophic subaortic stenosis, is seen in people with hypertrophic cardiomyopathy.