Mitral valve prolapse (MVP) occurs when one of your heart's valves doesn't work properly. The flaps of the valve are "floppy" and don't close tightly. Most people who have the condition are born with it. It also tends to run in families.

The mitral valve is a valve that lets blood flow from one chamber of the heart, the left atrium, to another called the left ventricle. In mitral valve prolapse, part of the mitral valve slips backward loosely into the chamber called the left atrium. This happens when the main heart muscle, called the left ventricle, squeezes during each heartbeat.

In mitral valve prolapse, the valve slips backward due to the abnormal size of or damage to the mitral valve tissues. For most people with mitral valve prolapse, the cause is unknown.

Mitral valve regurgitation — also called mitral regurgitation, mitral insufficiency or mitral incompetence — is a condition in which your heart's mitral valve doesn't close tightly, allowing blood to flow backward in your heart. Thus, blood can't move through your heart or to the rest of your body as efficiently, making you feel tired or out of breath.