The extents of mitral leaflet opening and closure are determined by left ventricular systolic function.

Correspondence to: Sanjiv Kaul, MD, Cardiovascular Division, Box 800158, Medical Center, University of Virginia, Charlottesville, VA 22908-0158, USA; [email protected] . . . . . . . . . . . . . . . . . . . . . . . I n order to appreciate the spatiotemporal relation between the mitral leaflets and mitral annular plane during the cardiac cycle, one has to begin with the ‘‘neutral’’ position of the mitral leaflets in relation to the mitral annular plane. This can be defined as the position of the mitral leaflets when there is no pressure difference between the left atrium and left ventricle. If the annulus were a Euclidean plane, the neutral position of the leaflets would be in the plane of the annulus (fig 1A). Because the mitral annulus is saddle shaped the neutral position of the mitral leaflets is not in the Euclidean plane but is caudal to it (fig 1B). This position results from the tension on the leaflets by the saddle shaped annulus which affords them a spring-like quality so that a greater force is required to move them cephalad towards the mitral annular plane than to move them caudally further into the left ventricular (LV) cavity (fig 1B).