The mitral valve is a two-flapped heart valve between the left atrium and left ventricle of the heart. Its function is to keep the blood flowing in one direction through the left side of the heart, and to prevent backflow of blood when the heart contracts.
The mitral valve is named for its shape, which resembles a tall bishop's hat called a mitre. It is made up of two triangular-shaped fibrous membranes, thin but tough, which are attached to strong cords like parachute cords, in turn attached to muscles. When the heart contracts, the two leaves billow up to close off the opening between the upper atrium and the lower ventricle on the left side of the heart.