Causes of Heart Murmurs

There are many possible causes of heart murmurs, and they vary depending on the type of murmur a person has. For example, innocent (harmless) murmurs may be caused by things such as faster blood flow or increased amounts of blood flowing through the heart. Causes of abnormal heart murmurs include congenital defects, calcification of the heart's valves, and certain illnesses.

Causes of Innocent Heart Murmurs

Innocent (harmless) heart murmurs are heard when blood moves noisily through a normal heart.
Some of the innocent heart murmurs causes include:
  • A faster-than-usual flow of blood through the heart and blood vessels attached to the heart
  • An increased amount of blood flowing through the heart
  • Illnesses or conditions that can cause blood to flow faster than usual through the heart, including fever, anemia, and too much thyroid hormone in the body (hyperthyroidism).
Innocent murmurs are sometimes due to changes in the heart due to heart surgery or aging.
Causes of Innocent Heart Murmurs in Children and Pregnant Women
Many, if not most, children will have a heart murmur heard by their doctor at some time in their lives. Besides childhood, the most common period of time for an increased amount of blood to flow through the heart is during pregnancy. Most murmurs found in pregnant women are innocent. They are due to the extra blood women's bodies make while they are pregnant.

Causes of Abnormal Heart Murmurs

The most common cause of abnormal heart murmurs is congenital heart disease. Congenital heart disease occurs when the heart, heart valves, or blood vessels attached to the heart do not develop normally before a baby is born. Some babies are born with a combination of heart defects.
Common defects that cause heart murmurs include:
  • Congenital septal defects, which are holes in the wall (septum) that separates the right and left sides of the heart. This type of defect accounts for more than half of all abnormal murmurs in children.
  • Congenital valve defects, which include narrow valves that do not allow enough blood to flow through them and leaking valves that do not close properly.
  • Calcification (hardening and thickening) of valves as a result of aging. The hardened and thickened heart valves do not work as they should.
  • Infections and other conditions that damage heart valves or other structures of the heart may also cause heart murmurs. These include:
o Rheumatic fever, a serious illness that can develop after a person has an untreated or incompletely treated infection caused by the bacteria that cause "strep" throat or scarlet fever. Rheumatic fever can lead to permanent damage to the heart. If your doctor diagnoses strep throat, be sure to take all of the antibiotics prescribed, even if you feel better before the antibiotics run out.
o Endocarditis, an inflammation of the inner lining of the heart and valves that is usually caused by a bacterial infection. Endocarditis is a serious disease that can lead to permanent heart damage and other complications. Endocarditis usually occurs in an abnormal heart.
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Information on Heart Murmurs

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