To understand what a heart murmur is, it's important to first know that hearts typically make two sounds: one made when valves close after blood enters the heart, and another after blood is ejected and delivered to the rest of the body. "A heart murmur is a sound which is created by the flow of blood. It may be innocent, or indicative of an underlying abnormality," says Stephen W. Kopf, M.D., cardiologist and associate director of the cardiovascular department at Phelps Memorial Hospital Center in Sleepy Hollow, New York. It's the extra sound heard between the rhythmical "lub dub" of a normal heart, which is the result of it contracting and relaxing as blood flows back to the heart.
Up to 23 percent of newborns have a murmur that turns out to be benign -- called "innocent" -- and disappears in 98 percent of babies by 6 months of age, according to the American Academy of Pediatrics. "Innocent murmurs are just the extra sounds the heart makes when blood flows across an opening or through a blood vessel fast enough to make noise," says Mark Alexander, M.D., a specialist in cardiology at Boston Children's Hospital and assistant professor of pediatrics at Harvard Medical School.
Innocent murmurs usually occur in an immature heart that has a large amount of blood flowing through normal arteries and veins that, like the rest of the infant or child, are still quite small and close to the stethoscope; they must grow into their role of handling the rapid blood flow through the heart. There are three types of innocent murmurs: In a Still's murmur, the most common type, the sound will be louder when the child lies down; it is often described as musical. A peripheral pulmonary stenotic murmur is usually a high-pitched "blowing" sound and can often be heard 24 hours after birth; it's most often picked up during a child's first well visit. A venous hum is typically heard at the neck and below the clavicles and is characterized by a buzzing sound that gets louder as a child stands.
Some murmurs may be the result of obstruction or abnormal connections in the heart. Murmurs that are associated with significant difficulties with feeding, breathing, or poor color may be a sign of either important heart disease or other significant medical problems. These are some of the red flags.
Murmurs that are grade 3 or higher.
Doctors typically grade murmurs on a scale of 1 to 6, based on their loudness, with innocent murmurs usually falling somewhere between 1 and 2. Murmurs that are grade 3 or higher may be more concerning.
Murmurs that are harsh.
"Small ventricular septal defects can produce very loud murmurs because the blood goes from a high- to a low-pressure area," Dr. Alexander explains. "For the tiniest septal defects, the murmur is so typical we often don't do any testing. We describe these murmurs as 'harsh.'"
Murmurs that last through most of the heartbeat.
These are called pansystolic murmurs. When a heart contracts or squeezes out its blood supply to be delivered to the body, most of the blood flows through the aorta, or main pipe, that feeds the rest of the arteries that supply the organs. If there is a hole or defect somewhere with the heart, the force of the contraction will squeeze some of the blood through that opening, creating the sound.
If your doctor is worried about a murmur, he will usually have you see a pediatric cardiologist. That visit will involve an electrocardiogram (ECG or EKG), another exam to listen to the murmur, and possibly an ultrasound of the heart (an echocardiogram). None of these tests are dangerous. The cardiologist can quickly determine whether the murmur is innocent, represents a mild abnormality, or is a sign of more significant heart disease.
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