Located between the upper left chamber and lower left chamber of the heart, the mitral valve is made of two flaps of tissue that normally open and close in a rhythmic way to allow blood to flow in one direction--from the atrium (upper chamber) to the ventricle (lower champer). The left ventricle is responsible for much of the heart's pumping and propels oxygen-rich blood into the arteries. The arteries then carry the blood throughout the body. When the mitral valve doesn't open and close properly, the flaps may "billow" backward slightly into the upper chamber during the heart's contraction (fig. B). This is called mitral valve prolapse (MVP). As a result of MVP, a clicking sound can often be heard by the doctor listening to the heart sounds with a stethoscope.

In MVP, sometimes small amounts of blood may leak backward into the upper chamber of the heart because the valve does not close normally. This causes a "heart murmur," although the heart itself is working normally. The heart has an adequate blood supply, even with the MVP. Prolapsing mitral valves do not usually get worse over time.

Mitral valve prolapse is the most common cardiac problem and may affect five to twenty percent of the population. The condition is most common in women, although men are also affected. With MVP, symptoms do not begin before the early teenage years (approximately age 14 in girls and 15 in boys), but adults of any age may be affected. MVP tends to run in families, so those with blood relatives with MVP have a greater chance of also having the condition. The mitral valve prolapse syndrome is sometimes called dysautonomia. Click here to learn more about dysautonomia .