A "bump-bump, bump-bump" sound is what is usually heard when listening to the heart. A heart murmur is an extra sound. There are many types of extra sounds that may be heard, but all of them go under the heading of murmurs. Many factors may cause murmurs in children, and the condition can be benign or quite serious.

It is estimated that at least 85 percent of babies will have a murmur during the first 24 hours after birth. This is caused by the normal closure of a blood vessel and usually goes away within 48 hours.

Older children also develop heart murmurs, but the vast majority are benign and will tend to come and go, although up to 15 percent will retain this sound into adulthood. These are termed innocent murmurs. It is felt that the sounds are caused by the eddies that form from the blood being squeeezed out of the heart. In other words, these murmurs are caused by turbulence of blood flow -- not by a defect in the heart -- and are of no significance except to cause anxiety in the parent.

Another innocent murmur is caused by a normal narrowing of the blood vessels in the lungs. The sound is produced much in the same manner as when you put your thumb over a garden hose to make the stream faster. Thus, a "heart" murmur may actually be a sound not coming from the heart, but from blood vessels near the heart. There are several other types of innocent murmurs, but the important point is that they cause no problems.

Murmurs caused by defects in the heart are termed pathologic. The most common of these in children is the ventricular septal defect (VSD), which is a hole in the wall of two particular chambers of the heart making a connection between the chambers that shouldn't be there. When the blood flows through this connection, it makes a sound.

Other pathologic murmurs may be caused by defects in the valves of the heart or other connections that shouldn't be there. The abnormal enlargement of the heart muscle is another defect which tends to cause new murmurs in adolescents. As with the innocent murmurs, there are many different types of pathologic murmurs. Most require surgical correction.

Your four-day-old most likely has an innocent murmur, if it is the kind caused by the narrowing of the blood vessels in the lungs as described above. This is a quite common murmur. However, if its sound is not typical of this murmur, it may be of the pathologic type. This is impossible to know without listening.

One of the most important things your doctor will check is how well your daughter is growing. Many pathologic murmurs will slow growth because the defect make the heart expend the energy used to sustain growth simply to supply adequate blood and oxygen to the body.

Most innocent murmurs are easily diagnosed just by listening and making sure your daughter is otherwise healthy. If there is any question, you can expect your doctor to order an electrocardiogram (EKG). If there is still a question as to whether the murmur is innocent, your doctor may consult a cardiologist, who will order an echocardiogram (an ultrasound of the heart).