Figure 1).

Left ventricular contraction. Figure represents diastole (external dashed lines) and systole (shaded figure). Stroke volume is determined from the difference in internal end-diastolic and end-systolic volumes. It is also determined by the change in total external volume assuming the myocardium is incompressible. Therefore, the stroke volume is the sum of the volume of atrioventricular displacement (red arrows) and is disc shaped. In addition, there is a smaller contribution from external epicardial displacement (blue arrow heads) and is approximately cylindrically shaped). Note that epicardial fractional shortening is less than midwall fractional shortening and midwall fractional shortening is less than endocardial fractional shortening (green arrows)