The mitral valve is the heart valve between the left atrium and left ventricle. It has two flaps, called leaflets or cusps, which open and close when the heart contracts (beats) and rests.

Mitral-valve prolapse (MVP) is frequently diagnosed in healthy people and is, for the most part, harmless. Most people suffer no symptoms at all. New estimates are that about 2 percent of the adult population has the condition. MVP is also called floppy valve syndrome, Barlow's or Reid-Barlow's syndrome, ballooning mitral valve, midsystolic-click-late systolic murmur syndrome, or click murmur syndrome. MVP can be present from birth or develop at any age and occurs equally in both men and women. MVP is one of the most frequently made cardiac diagnoses in the United States.

The heart's valves work to maintain the flow of blood in one direction, ensuring proper circulation. The mitral valve controls the flow of blood into the left ventricle. Normally, when the left ventricle contracts, the mitral valve closes and blood flows out of the heart through the aortic valve and into the aorta to start its journey to all other parts of the body.

In MVP, the shape or dimensions of the leaflets of the valve are not ideal; they may be too large and fail to close properly or they balloon out, hence the term "prolapse." When the valve leaflets flap, a clicking sound may be heard. Sometimes the prolapsing of the mitral valve allows a slight flow of blood back into the left atrium. This is called "mitral regurgitation," and may cause a sound called a murmur. Some people with MVP have both a click and a murmur and some have only a click. Many have no unusual heart sounds at all; those who do may have clicks and murmurs that come and go.

The vast majority of people with MVP have no discomfort at all. Most are surprised to learn that their heart is functioning in any way abnormally. Some individuals report mild and common symptoms such as shortness of breath, dizziness, and either "skipping" or "racing" of the heart. More rarely, chest pain is reported. However, these are symptoms that may or may not be related to the MVP.

In most cases, no treatment is needed. For a small proportion of individuals with MVP, beta-blockers or other drugs are used to control specific symptoms and some blood pressure lowering drugs may be used to treat mitral regurgitation. Serious problems are rare, can easily be diagnosed and, if necessary, treated surgically.