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Causes
By Mayo Clinic staffThere are two types are heart murmurs: innocent murmurs and abnormal murmurs. A person with an innocent murmur has a normal heart. This type of heart murmur is common in newborns and children. More than half of all children have heart murmurs at some time, and most of those murmurs are harmless.
An abnormal heart murmur is more serious. In children, abnormal murmurs are usually caused by congenital heart disease. In adults, abnormal murmurs are most often due to acquired heart valve problems.
Innocent heart murmurs
An innocent murmur can occur when blood flows more rapidly through the heart. Conditions that may cause rapid blood flow through your heart, resulting in an innocent heart murmur, are:
- Physical activity or exercise
- Pregnancy
- Fever
- Anemia, in which there aren't enough healthy red blood cells to carry adequate oxygen to your body tissues
- Hyperthyroidism, an excessive amount of thyroid hormone in your body
Changes to the heart due to aging or heart surgery also may cause an innocent heart murmur. Over time, innocent heart murmurs may disappear, or last your entire life without ever causing further health problems.
Abnormal heart murmurs
Although most heart murmurs aren't serious, some may result from a heart problem. The most common cause of abnormal murmurs in children is congenital heart disease — when babies are born with structural heart defects. Common congenital defects that cause heart murmurs include:
- Holes in the heart or cardiac shunts. Many heart murmurs in children are the result of holes in the walls between heart chambers, known as septal defects. These may or may not be serious, depending on the size of the hole and its location. There are two types of septal defects. A ventricular septal defect is a hole between the lower chambers of the heart. Atrial septal defects are holes between the upper chambers. Shunts occur when there's an abnormal blood flow between the heart chambers or blood vessels, leading to a heart murmur.
- Heart valve abnormalities. Congenital heart valve abnormalities are present at birth, but sometimes aren't discovered until much later in life. Examples include valves that don't allow enough blood through them (stenosis) or those that don't close properly and leak (regurgitation).
Other causes of abnormal heart murmurs include infections and conditions that damage the structures of the heart and are more common in older children or adults. For example:
- Rheumatic fever. Although rare in the United States, rheumatic fever is a serious inflammatory condition that can occur when you don't receive prompt or complete treatment for a strep throat infection. In many cases, rheumatic fever may permanently affect the heart valves and interfere with normal blood flow through your heart. Prompt and proper treatment of strep throat with antibiotics can prevent strep throat from progressing to rheumatic fever.
- Endocarditis. This is an infection and inflammation of the inner lining of your heart and valves. Endocarditis typically occurs when bacteria or other germs from another part of your body, such as your mouth, spread through your bloodstream and lodge in your heart. Left untreated, endocarditis can damage or destroy your heart valves. This condition usually occurs in people who already have heart abnormalities.
- Valve calcification. This hardening or thickening of valves, called mitral or aortic valve stenosis, can occur as you age. These valves may not work as well as they once did, making it harder for blood to flow through your heart, resulting in murmurs.
- Mitral valve prolapse. In this condition, the valve between your heart's left upper chamber (left atrium) and the left lower chamber (left ventricle) doesn't close properly. When the left ventricle contracts, the valve's leaflets bulge (prolapse) upward or back into the atrium, which may cause a murmur. This condition is sometimes present at birth, but not detected until adulthood.
