The mitral valve is an essential valve between the left atrium and left ventricle, and it controls blood flow between them. The mitral valve allows blood to flow forward from the left atrium into the left ventricle, but restrict backward flow. On the right side, the heart has a right atrium and ventricle, where blood flow controlled by the tricuspid valve.

Mitral valve prolapse is a condition of the heart, in which the valve between the left atrium and ventricle of your heart fail to close correctly. Your mitral valve made up of two triangular-shaped flaps of tissues known as leaflets. These leaflets connect to the cardiac muscle through a ring known as the annulus. 

In mitral valve prolapse the leaflets of your valve bulge back into the atrium or upward when the heart contracts. With time, this leads to leakage of blood into the atrium. This is called mitral valve regurgitation, where the oxygenated and deoxygenated blood gets mixed before circulation to the body.

Usually, mitral valve prolapse might not require treatments or changes in lifestyle, if only a small amount of blood gets leaked into the atrium. It might not always be life-threatening. However, some people might need treatment.
People who develop symptoms of congestive heart failure caused by mitral valve prolapse with mitral regurgitation due to mitral valve prolapse, the surgery remain the treatment of choice. Valve surgery includes mitral valve repair and valve replacement.