
medical specialties at cardinal glennon children's in st. louis 

 Heart murmurs in children 

A heart murmur is a noise that the blood makes as it flows through the heart.  Typically blood flows silently.  It is when blood starts to flow more rapidly that noise is produced, which can be heard by listening with the stethoscope and is called "heart murmur." A heart murmur does not mean that there is anything wrong with your child's heart. Heart murmurs are common in children and are usually harmless. These noises are commonly heard in children because their hearts are very close to their chest walls.

Is there more than one kind of heart murmur?

Heart murmurs can be normal or abnormal.

  • Normal (innocent) heart murmurs:   The heart murmur does not reflect abnormalities of the heart. They can be heard in 50% of children most frequently from 3-8 years of age but can be heard in infants and toddlers as well.

  • Abnormal (pathologic) heart murmurs:  Sometimes a heart murmur indicates a problem with the structure of the heart. Problems that can cause this type of heart murmur include a hole in the heart or a leaky or narrow heart valve.

What causes a normal (innocent) heart murmur?

Many normal conditions may cause the blood to flow more rapidly leading to a heart murmur.  These conditions do not indicate any problem and cause no harm to your child’s health. Heart murmurs caused by these conditions are called innocent murmurs.  An innocent murmur can get louder or softer depending on your child's heart rate, such as when they're excited or have fever. Many innocent murmurs become hard to hear as children grow older, and most usually go away on their own.

Some of the conditions causing an innocent heart murmur are:

  • Small blood vessels to the lungs (pulmonary arteries) in newborn children (Peripheral Pulmonary Stenosis or PPS):  Newborn babies have small blood vessels to the lungs. This is because while they were in their mother’s womb, there was very little blood flow to the lungs since babies do not breathe prior to birth.   This will cause the blood vessels to the lungs to be small (since blood flow causes blood vessels to grow).  Once the child is born, blood flow increases tremendously to the lungs; this will cause blood to be turbulent as it crosses these relatively small blood vessels and this turbulence will produce a heart murmur.  This type of murmur disappears at about 2 to 6 months of age.

  • Still's murmur (Vibratory murmur) and pulmonary valve (Physiologic pulmonary flow murmur):  Blood flow causes a vibration of the heart valves, or muscle strands inside the heart that can be heard when listening to the heart.  This is not because there is anything wrong with these heart valves or heart structure;  it may be due to the fact that children have a faster heart rate, which means that blood normally travels with a higher speed causing noise, resulting in the heart murmur. Also, children have thinner chest walls, which allow sounds to be more easily audible.

  • Venous hum: Sometimes, blood flow through large veins close to the skin surface in the neck and upper chest can be heard.

  • Mammary soufflé:  Developing breasts in normal teenage girls may cause the blood flow in the arteries providing blood to the developing breast tissue to be heard.

How can a doctor tell the difference between normal (innocent) or abnormal (pathologic) heart murmurs?

Innocent heart murmurs have certain features which can be easy to detect by the examination.   Some tests may be done to confirm the fact that there is no heart disease such as an electrocardiogram (ECG), chest x-ray or an echocardiogram (ultrasound of the heart).

What does it mean if my child has an innocent heart murmur?

An innocent heart murmur does not pose a health threat. If your child has an innocent heart murmur, he or she can run, jump and play, with no limitations to activity. Your child doesn't need to take any medicine or be careful in any special way.

Will my child outgrow an innocent heart murmur?

As the child grows older the chest wall gets thicker and the heart rate slows down so the innocent heart murmurs can no longer be heard. Sometimes innocent murmurs are heard in to adulthood but they remain harmless. 


American Heart Association: Heart Murmur

Nation Heart, Lung and Blood Institute

Thomas Biancaniello, MD. Innocent Murmurs. Circulation. 2005; 111:e20-e22.




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