DEAR DOCTOR K:

I have mitral valve prolapse. What does this mean? And why don't I need treatment for it?

DEAR READER

The heart is made up of four chambers. Normally, the upper two chambers (the atria) fill with blood, then pump blood into the lower two chambers (the ventricles). Next, the ventricles pump blood to the rest of the body.

The mitral valve is the physical doorway between the heart's left atrium and left ventricle. The valve has two leaflets.

When it's working properly, the mitral valve opens to let blood flow "forward" -- from the left atrium down into the left ventricle. The two leaflets drop down into the left ventricle. But when the left ventricle then pumps the blood out to the body, the mitral valve closes, to prevent blood from flowing "backward" up into the left atrium. The two leaflets are directly between the left atrium and left ventricle.

In mitral valve prolapse, however, a slight deformity of the mitral valve prevents the valve from closing normally. This appears as an abnormal floppiness, or prolapse, of the valve. When the left ventricle pumps, the two leaflets get pushed back up into the left atrium. (I've put an illustration of a prolapsed mitral valve on my website, AskDoctorK.com.)

The result is that small amounts of blood leak back into the left atrium. It sounds serious, but in most people it actually has very little effect on the heart's overall ability to pump blood.

In some people, however, the leak worsens to create a significant backward flow of blood into the left atrium. This is called mitral regurgitation. People with severe mitral regurgitation can develop shortness of breath, fatigue and leg swelling.

Mitral valve prolapse is a lifelong condition, but most people who have it never have symptoms. The condition is discovered only when a doctor hears a certain clicking sound during a routine physical examination. This abnormal heart sound is related to the malfunction of the mitral valve.

If you have mitral valve prolapse but do not have any symptoms, you will not need treatment. In the past, doctors recommended that people with mitral valve prolapse take antibiotics prior to certain surgical procedures and dental appointments, but the American Heart Association no longer recommends this.

If mitral valve prolapse develops into severe mitral regurgitation, you may need to have the abnormal mitral valve surgically repaired or replaced.

Mitral valve prolapse has almost surely been present in human beings for tens of thousands of years, but we discovered it only about 50 years ago. Initially, doctors worried that it was a serious, even life-threatening, condition. However, as has been true of many newly discovered conditions and diseases, we first recognize it in the people who have the most severe forms of it. As we find out more about it, we learn that many people with the condition have nothing to worry about.

(Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.)

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