The mitral valve is the valve that allows flow from the Left Atrium to the Left Ventricle.  It is also referred to as the bicuspid valve.  Together with the tricuspid valve, they are collectively called the atrioventricular valves because they lie between the atria and ventricles on their respective sides.

 Mitral Valve Prolapse (MVP)

In MVP, the mitral valve does not close properly due to the displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole.