A heart murmur is an extra or abnormal sound that happens when the heart pumps blood. Your child's healthcare provider can hear the murmur when listening to your child's heart with a stethoscope. Heart murmurs are common in children, and are most often a normal part of their growth. At some point, just about every child will have a heart murmur. A heart murmur usually doesn't mean that your child has a serious health issue. But in rare cases, a heart murmur can be a sign of a serious condition. That's why it's important for your child to see a cardiologist. A cardiologist can find out if your child's murmur is caused by a problem in his or her heart, or if it's nothing to worry about.