Mitral valve leaflets (anatomy)

Usually, there are two mitral valve leaflets giving rise to the alternative name for the valve - bicuspid. The cusps are commonly held to be anterior and posterior. However, it would be more appropriate to consider the leaflets as the interruption of an otherwise continous sheet around the orifice by two incomplete clefts, the anterolateral and posteromedial commissures.

Points of note:

• during diastole, they project into the ventricle and are widely separated from each other
• each has a central, collagenous lamina fibrosa that is continuous with the fibrous annulus of the valve
• the lamina fibrosa is surrounded by endocardium
• the endocardium is continuous at the edges of the valve on the ventricular side with the chordae tendineae
• the surface of each leaflet is irregular at its edge due to the presence of numerous 'clefts' - most chordae tendinae insert into this roughened zone from the ventricular side of the valve
• the leaflets of the mitral valve have a smaller cross-sectional area and are stiffer than the tricuspid leaflets; consequently, they are displaced to a relatively lesser extent into the atrium when the valve closes

There is much confusion in the nomenclature of the leaflets largely due to the oblique positioning of the plane of the valve - this is discussed in the submenu.

Occasionally, the anterior and posterior leaflets may fail to coapt; a small accessory leaflet may bridge the gap.