The outer contour of the heart has in some studies been shown to be constant during the heart cycle and the epicardial apex almost stationary whilst the base of the ventricles moves towards apex during systole. The base of the left ventricle has been regarded as a cylinder with constant cross-sectional area with changes in height during the heart cycle, the latter corresponding to the amplitude of mitral annulus motion (MAM). In this echocardiographic study, including 20 healthy adults, the stroke volume calculated by the cylinder model was significantly lower than by a reference method (modified Simpson's rule). MAM explained 82% of the stroke volume and 18% must, therefore, be explained by an inward motion of the outer left ventricular wall. A mean outer diameter shortening of about 3% (about 2 mm) was calculated.