Hemodynamic responses to the Valsalva maneuver were studied in eight healthy subjects (group 1) and eight patients with ASD (group 2) using Doppler echocardiography. The acute changes of aortic blood flow profiles during the Valsalva maneuver were investigated on a basis of beat-to-beat estimation. During the active strain phase (phase 2), group 1 showed a significant decrease in systolic blood pressure, SV and CO with reflex tachycardia; in group 2, there was a significant decrease in SV and CO with reflex tachycardia, but not systolic blood pressure. The percentage decreases in SV and CO in group 2 were significantly less than those in group 1 (23 +/- 16 percent vs 48 +/- 10 percent for SV, p less than 0.01; 17 +/- 12 percent vs 40 +/- 13 percent for CO, p less than 0.05). After release of strain phase (phase 4), group 1 showed significant reversed changes in systolic blood pressure, SV and heart rate, indicating an overshoot effect which was, however, not observed in group 2. Thus, patients with ASD presented abnormal Valsalva response which was characterized by the absence of phase 4 overshoot and a less marked phase 2 change. The findings suggest that the decremental effect of impaired venous return on stroke output during active strain may be attenuated by the increased pulmonary blood volume due to left-to-right shunt. In patients with ASD, the lesser decrement of CO during phase 2 may not provoke sufficient sympathetic activity to induce overshoot response in phase 4.