Murmurs in Children and Adolescents
Doctors use the term "heart murmur" to refer to almost any sound the heart makes when pumping the blood. Although people think of heart murmurs as a problem, most heart murmurs in children are completely normal, and are only the usual sound of blood flowing through a normal heart. Normal heart murmurs, also known as "innocent murmurs" or "functional murmurs", occur in about 40% of children, and tend to come and go throughout childhood. General pediatricians and family practitioners have a lot of experience with these sorts of murmurs. Examples include the innocent Still's murmur, innocent PPS murmur and innocent venous hum.
On the other side of the coin, about 1% of all children actually do have heart abnormalities. Most of these abnormalities are quite minor, but some are serious. When a physician caring for a child hears a heart murmur, and they are not sure whether it is an innocent murmur or not, they often refer the family to a pediatric cardiologist (children's heart specialist). The pediatric cardiologist can often tell if a murmur is innocent just by listening, or may perform one or more tests to sort things out. In my pediatric cardiology practice, most children sent to me because of a heart murmur have innocent murmurs (nothing wrong with them), about a quarter have minor heart abnormalities, and fewer than 5% have a serious heart condition.
Here are some Internet links that might be helpful. They look pretty good, but I cannot vouch for their accuracy or quality. As always with the Internet, browser beware!
American Heart Association: Innocent Murmurs
American Academy of Family Physicians - Heart Murmurs in Children--What Parents Should Know
Pennsylvania Children's Hospital: Heart Murmurs
iVillage: Are Infant Heart Murmurs Common?
The Nemours Foundation: Heart Murmurs