What is a heart murmur?

Heart murmur is the noise made by blood as it travels through the heart, similar to the noise made by water as it run from a faucet.  Blood flow in normal circumstances flow silently.  It is when blood starts to flow turbulently that noise is produced, which could be hear by auscultation and is termed "heart murmur".

Is there more than one kind of heart murmurs?

Heart murmur could be normal or abnormal.
Normal (innocent) heart murmurs:  This is heard in about 50% of all normal infants.  It does not reflect abnormalities of the heart.
Abnormal (pathologic) heart murmurs:  This is heard in patients with heart disease in which there is an abnormal structure of the heart, making blood travel in an abnormal fashion resulting in a noise also known as heart murmur.  Heart diseases causing murmur include abnormal heart valves which are too tight (stenosis) or leaky (regurgitation).  Other heart diseases which produce heart murmurs include abnormal communications within the heart (holes in the heart such as atrial septal defect ASD, ventricular septal defect (VSD), or abnormal communication between blood vessels such as patent ductus arteriosus (PDA).

Normal Heart Cycle
The ventricles contract to propel blood out through the aorta and pulmonary arteries to the body and lungs.

What causes a normal (innocent) heart murmur?

Many conditions, all within normal limits, may cause the blood to flow with turbulence leading to a heart murmur on auscultation.  All these conditions do not indicate any abnormality and cause no ill effect on ones health.  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 mothers' uterus, there was very little blood flow to the lungs since babies do not breath 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, this turbulence will produce a heart murmur.  This disappears at about 2 months of age.

Normal Blood Flow
Normally the blood flows smoothly and silently .

Blood flow through the aortic valve (Still's murmur) and pulmonary valve (Physiologic pulmonary flow murmur):  Blood flow across these two valves is audible in some children.  This is not because there is anything wrong with these valves, but 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 allows sounds to be more readily audible.
Venous hum: Sometimes, blood flow through large veins close to the skin surface in the neck and upper chest could be audible.

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 audible.

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

Innocent heart murmurs have certain features which are easy to detect by the examining doctor. 

  First the doctor would ask questions to see if there are any suggestions of heart disease such as problems soon after birth, does the child feed well, any fatigue or shortness of breath from exercise typically tolerated of other children of the same age, and finally any history of bluish discoloration of the child's lips.  These are features suggesting of heart disease, which if present may suggest that the heart murmur is pathologic and not innocent.

  Then the doctor would try to illicit any signs of heart disease when examining the child.   Abnormal findings suggesting heart disease such as evidence of congested lungs or liver, or swelling of extremities, or bluish discoloration of lips or other mucosa may suggest heart disease.
 

Abnormal Blood Flow
In this example there is pulmonary valve stenosis.  The small pulmonary valve orifice causes the blood to be turbulent and noisy which is heard as a heart murmur on auscultation.

Will my child outgrow an innocent heart murmur?

If a child has an innocent heart murmur, then the heart is normal and there is nothing to outgrow.  However, the murmur may after few years be no longer audible as the chest wall gets thicker and the heart rate slows down.