The vast majority of heart murmurs in children are socalled “innocent murmurs,” which are part of normal development, require no treatment and usually will become softer with time and eventually disappear.

“Innocent murmurs, also sometimes called ‘functional’ murmurs, are common in children. About 35 percent of infants have innocent murmurs, and more than 50 percent of children going into preschool and kindergarten may have this type of murmur noted on at least one occasion,” says Dr. William Scott, interim chief of cardiology at Children’s Medical Center. The murmurs are present because of normal changes in blood flow through the growing heart. The thinness of a young child’s chest wall enables a physician to hear clearly the child’s blood as it is pumped through the heart.

“There’s very little distance between our stethoscope and the children’s hearts because they have less muscle, their skeleton is primarily cartilage and their lungs are small, so we can more easily hear these normal sounds,” Dr. Scott explains.

Innocent murmurs are more noticeable when the heart rate is higher, such as during an illness, fever or due to the anxiety of being in a doctor’s office worrying about getting a shot.

“I reassure parents that innocent murmurs are normal sounds of the heart and not to panic about them,” he says.

Occasionally, children do have a significant murmur related to an abnormality of the heart – but it is typically distinct from an innocent murmur. Murmurs associated with serious heart problems usually make different sounds that often begin and end during a different part of each heart beat. Other problems frequently accompany abnormal heart murmurs, including trouble putting on weight in relation to increase in height. Most structural defects are detected before a child’s first birthday.

Despite the frequency of innocent murmurs, children with heart murmurs often are referred to a specialist, such as Dr. Scott, to rule out any serious problem.