There are two types of 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.

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 than normal through the heart. Conditions that may cause rapid blood flow through your heart, resulting in an innocent heart murmur, include:

  • Physical activity or exercise
  • Pregnancy
  • Fever
  • Not having enough healthy red blood cells to carry adequate oxygen to your body tissues (anemia)
  • An excessive amount of thyroid hormone in your body (hyperthyroidism)
  • Phases of rapid growth, such as adolescence

Innocent heart murmurs may disappear over time, or they may last your entire life without ever causing further health problems.

Abnormal heart murmurs

The most common cause of abnormal murmurs in children is when babies are born with structural problems of the heart (congenital heart defects).

Common congenital defects that cause heart murmurs include:

  • Holes in the heart or cardiac shunts. Known as septal defects, holes in the heart may or may not be serious, depending on the size of the hole and its location.

    Cardiac shunts occur when there's an abnormal blood flow between the heart chambers or blood vessels, which may lead 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), such as mitral valve prolapse.

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:

  • Valve calcification. This hardening or thickening of valves, as in mitral stenosis or aortic valve stenosis, can occur as you age. Valves may become narrowed (stenotic), making it harder for blood to flow through your heart, resulting in murmurs.
  • Endocarditis. This infection of the inner lining of your heart and valves 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 valve abnormalities.

  • Rheumatic fever. Although now rare in the United States, rheumatic fever is a serious condition that can occur when you don't receive prompt or complete treatment for a strep throat infection. It can permanently affect the heart valves and interfere with normal blood flow through your heart.
April 03, 2015