Chances are that at least one member of your family has been told at some point that he or she has a murmur. What exactly does this mean?

• Is it dangerous?
• Can it be passed along through families?
• Why wasn’t it heard earlier?
• Is it safe to do strenuous exercise?
• Do you need to take an antibiotic at the dentist?

Before we get to these questions, let’s start with a little background. At birth the human heart is approximately the size of a walnut. It mirrors the size of our fist as we grow, reaching the size of an orange or grapefruit when we become adults.

The purpose of the heart is to pump blood around our body in order to deliver oxygen and nutrients to our muscles and organs. The way it is able to accomplish this is really quite amazing.

The heart contains four chambers and four heart valves. First, blood enters an empty chamber, then the heart valves leading into and out of the chamber close shut. As the heart muscle begins to squeeze, the size of the chamber becomes smaller and smaller. With no way for blood to get out, the pressure within the chamber rises higher and higher until the valve leading out of the heart finally bursts opens and blood streams out of the heart. With one beat after another, the heart pumps blood forward at this high pressure, allowing it to circulate all the way around the body and back to the heart.

When you listen to the heart with a stethoscope, you will normally hear two or three crisp sounds, like the beat of a drum, with silence in between. These are the sounds of the four heart valves closing shut. A murmur is a sound heard in the period of silence before and after the valves close. The word murmur is just a general term for this extra sound. Murmurs can be soft or very loud, and usually make a “shhhhh” sound each time the heart squeezes.

If blood flows smoothly through the heart, there is no murmur. If the blood flow becomes turbulent, a murmur is produced. The turbulence can be caused by a variety of things, such as a fever, anemia, a hole in the heart, small or leaky heart valves, muscles narrowing the blood’s pathway through the heart, or narrowed blood vessels carrying blood away from the heart to the lungs or body.

By far, the most common type of murmur is an innocent murmur. These murmurs are produced by blood flowing through a perfectly formed heart. This is a completely normal phenomenon and occurs in 75 percent of children at some point during their childhood. Pediatricians performing physical examinations on children hear these murmurs hundreds of times every year. These murmurs come and go, and become louder during periods of fever, which is why they are often first heard during a sick visit. Because this type of murmur has a characteristic sound, many pediatricians will recognize the murmur as innocent and further evaluation is not necessary.

However, if the murmur sounds louder, harsher, or different in pitch or placement on the chest, the pediatrician may refer the child for further evaluation by a pediatric cardiologist. At this point, careful physical examination, an electrocardiogram (ECG) and, occasionally, a chest X-ray and an echocardiogram (ultrasound of the heart) are performed to evaluate the murmur further and determine if the murmur is caused by a heart defect.

Innocent murmurs are not dangerous, require no treatment and will disappear at some point during childhood. Murmurs caused by heart defects often require continued follow-up evaluations by the pediatric cardiologist and, occasionally, a heart catheterization procedure or heart surgery.

Keep in mind that three out of every four children (75 percent) have a murmur at some point in their life – while only one in 100 children (1 percent) are born with a heart defect. Murmurs are not passed along through families, but certain heart defects can be. Depending on the cause of the murmur, they may appear at any time during childhood.

The answer to the question, “Why wasn’t it heard earlier?” is usually that the murmur wasn’t present at prior evaluations, or the pediatrician considered the murmur to be innocent. As for exercise and antibiotics, innocent murmurs do not require exercise restrictions or antibiotics prior to dental procedures. Other types of heart defects that cause murmurs may require these, and the pediatric cardiologist will advise you in these situations.

Next time, we’ll discuss how physicians learned to diagnose the different heart defects by the murmurs they produced.

Laurie Armsby, M.D.
Associate Professor of Pediatrics, Division of Pediatric Cardiovascular Medicine
Pediatric Interventional Cardiologist
OHSU Doernbecher Children’s Hospital
OHSU Pediatric and Adult Congenital Cardiac Catheterization Lab