The sounds your doctor hears using a stethoscope while your heart beats are called heart murmurs.
"Innocent" heart murmurs
Innocent heart murmurs are sounds made by blood circulating through the heart’s chambers and valves, or through blood vessels near the heart. Innocent murmurs are common in children and are harmless. These heart murmurs may also be referred to as “functional” or “physiologic” murmurs.
A high percentage of children are likely to have had an innocent heart murmur at some time. Innocent murmurs may disappear and then reappear. When a child’s heart rate changes, such as during excitement or fear, these innocent murmurs may become louder or softer. This still doesn’t signal that the innocent murmur is cause for concern.
If your doctor hears a heart murmur when listening to your child’s heart, he or she may recommend additional testing to confirm that the murmur is innocent.
Unless testing suggests that further inquiry is warranted, no next steps may be necessary. With an innocent heart murmur, your child won’t need medication, and doesn't have a heart problem or heart disease. You don't need to pamper or restrict your child’s diet or activities. Your child can be as active as any other normal, healthy child.
Most innocent murmurs disappear when a child reaches adulthood, but some adults still have them.
Read more about innocent murmurs.
Other, non-innocent heart murmurs are often caused by defective heart valves. For example, a stenotic heart valve has a smaller-than-normal opening and can’t open completely. Or, a valve may also be unable to close completely. This leads to regurgitation, which is blood leaking backward through the valve when it should be closed.
Certain congenital defects as well as other conditions such as pregnancy, fever, anemia or thyrotoxicosis (a diseased condition resulting from an overactive thyroid gland) can also cause murmurs.
A murmur that occurs when the heart muscle relaxes between beats is called a diastolic murmur. A systolic murmur occurs when the heart muscle contracts.
Systolic murmurs are graded by intensity (loudness) from 1 to 6, with a stethoscope slightly removed from the chest. A grade 1 out of 6 is faint, heard only with a special effort. A grade 6 out of 6 (6/6) is extremely loud, and can be heard with a stethoscope even when slightly removed from the chest.
En español: Read about heart murmurs (PDF).