Echocardiograms of 12 healthy male subjects in the supine and sitting positions were obtained. The end-diastolic (EDD) and end-systolic (ESD) diameters of the left ventricle were measured, and the stroke volume was calculated as the cube of the diameter. A significantly (P less than 0.001) smaller stroke volume was found in the sitting rest position (67.1 ml) compared to the supine rest position (92.3 ml). During dynamic exercise, the stroke volume increase in the sitting position (29.7%) was considerably higher than in the supine position (13%). The shortening fraction showed no difference in the sitting and supine positions at rest and during dynamic exercise. The results demonstrate good agreement between the echocardiographic method and other noninvasive procedures.