The left atrioventricular valve is located in the inferior wall of the left atrium and it is attached to the atrioventricular orifice. It consists of two cusps, or flaps; an anterior cusp and a posterior one. This is the reason it is also called 'bicuspid' or 'mitral valve', because it resembles the top portion of a bishop miter. The two flaps project downwards into the cavity of left ventricle and close tightly during myocardial contraction (systole).
The right and left atrioventricular valve cusps are opened and closed by the cardiac muscle relaxation during diastole and the pressure of blood when the heart ventricles contract during systole, respectively. The chordae tendineae (tendinous chords) are attached to the edges of the flaps and to the papillary muscles, which are on the wall of ventricle. The function of the chordae tendineae and the papillary muscles is to prevent the cusps of the valve from collapsing and caving upwards by the blood pressure when the heart muscle contracts.
Function
The function of the mitral valve is to regulate the flow of oxygenated blood from the left atrium into the left ventricle. It blocks the blood flow during systole (contraction of myocardium) and opens to let it flow during diastole (relaxation). When the valve is damaged and does not work properly, there is mitral regurgitation, which is the backflow of blood from the left ventricle back into the atrium.
Below, left aspect of open left side of heart. You can see both chambers with the left atrioventricular valve in between.
