To determine the level of exercise for dynamic exercise echocardiography and to evaluate the changes of cardiac work loads in normal subjects, the authors performed M-mode echocardiography at rest and during 20° supine bicycle exercise in 10 normal subjects with good image of left ventricle. A special, self-made 20° supine exercise table was used on which the subject's chest could be immobilized to record echocardiograms during exercise. The recordings were always performed just below the tip of the anterior mitral leaflet. Interpretable left ventricular M-mode echocardiograms were obtained at a submaximal exercise level with mean heart rate of 132±21 beat/min. Left ventricular end-diastolic dimension, an index of preload, showed no significant change during exersise. But left ventricular end-systolic dimension decreased significantly(p<0.01) and % fractional shortening increased significantly(p<0.01). Peak-systolic left ventricular wall stress increased signficantly(p<0.01) during exercise but end-systolic wall stress did not. Both end-systolic wall stress/end systolic dimension ratio and systolic blood pressure/end-systolic dimension ratio increased during exercise(p<0.01).