The mitral valve is a “one way” bi-leaflet heart valve that lies between the left atrium and the left ventricle. When the left atrium contracts, the mitral valve opens allowing the blood to flow and fill the left ventricle. When the left ventricle contracts, the mitral valve will close, preventing blood from returning to the left atrium and forcing the blood being pumped to flow through the aortic valve, through the aorta, and deliver blood to all organs of the body.
If the valve leaflets don’t close (coapt) properly, a portion of the blood from the ventricular contraction flows backwards (regurgitates) into the left atrium.