Hypotension during dobutamine stress echocardiography is caused by ischemia as well as non-ischemic causes. Whether sigmoid interventricular septum seen in the aged can cause hypotension during dobutamine stress echocardiography was investigated in eight men and four women with sigmoid interventricular septum (aged 53 to 76 years, mean 67 +/- 7 years). At peak dobutamine dose, seven patients (group H) showed a hypotensive response (defined as 5 mmHg or greater decrease in systolic blood pressure from the peak systolic blood pressure; mean = - 17 +/- 13 mmHg), while five subjects (group N) did not. No subject showed regional wall motion abnormalities. Before dobutamine infusion, group H had smaller left ventricular end-systolic dimension (26 +/- 3 vs 30 +/- 3 mm) than group N, but no difference was found in left ventricular end-diastolic dimension (44 +/- 3 vs 47 +/- 4 mm), percentage fractional shortening (40 +/- 6% vs 34 +/- 7%), diastolic aorto-septal angle (82 +/- 10 vs 95 +/- 11 degrees), systolic aorto-septal angle (94 +/- 10 vs 101 +/- 11 degrees), peak left ventricular outflow velocity (1.3 +/- 0.2 vs 1.2 +/- 0.3 m/sec) or peak left ventricular outflow pressure gradient (7 +/- 2 vs 6 +/- 3 mmHg). Group H had a lower peak dobutamine dose than group N (33 +/- 8 vs 40 +/- 7 micrograms/kg/min), but under the peak dose of dobutamine infusion group H showed smaller left ventricular end-systolic dimension (20 +/- 3 vs 26 +/- 4 mm), systolic mitral annulus diameter (19 +/- 3 vs 23 +/- 2 mm), diastolic aorto-septal angle (72 +/- 16 vs 92 +/- 6 degrees), and systolic aorto-septal angle (84 +/- 12 vs 100 +/- 6 degrees), and higher heart rate (114 +/- 10 vs 79 +/- 16 bpm), percentage fractional shortening (53 +/- 8% vs 43 +/- 7%), peak left ventricular outflow velocity (3.2 +/- 0.8 vs 1.7 +/- 0.3 m/sec), and peak left ventricular outflow pressure gradient (43 +/- 23 vs 12 +/- 5 mmHg). In addition, systolic anterior motion of the mitral valve with septal contact developed in 86% of group H and 0% of group N. Thus, about half of the patients with sigmoid interventricular septum show hyperresponse to dobutamine and develop dynamic left ventricular outflow tract obstruction as well as systemic arterial hypotension even without regional left ventricular wall motion abnormalities.