Left ventricular performance was studied during isometric exercise in 17 patients with severe congestive heart failure, combining invasive hemodynamic and echo-Doppler techniques. Isometric exercise at 30% of maximum resulted in a decrease in stroke volume index (27.4 ± 7.1 to 22.7 ± 7.4 ml/m2), with a significant increase in heart rate from 81 ± 10 to 92 ± 14 beats/min and in systemic vascular resistance from 1827 ± 527 to 2372 ± 737 dyne · sec · cm-5. A significant rise in pulmonary capillary wedge pressure (18 ± 9 to 31 ± 10 mm Hg) was associated with a marked increase in mitral regurgitant volume (14 ± 11 to 27 ± 15 ml), calculated as the difference between total stroke volume obtained by two-dimensional echocardiography and forward stroke volume measured by pulsed Doppler at the aortic anulus. During isometric exercise, left ventricular end-diastolic and end-systolic volumes did not change markedly, but the total stroke volume tended to increase from 62 ± 13 to 67 ± 13 ml. The increase in mitral regurgitant volume induced by isometric exercise was correlated with the fall in forward stroke volume (r = 0.7, p < 0.01). Thus a rise in systemic arterial pressure induced by isometric exercise is associated with a decrease in cardiac performance attributable to redistribution of total left ventricular output with an increase in mitral regurgitation and a simultaneous decrease in forward cardiac output.