Patients with severe coronary artery disease (CAD) sometimes complain of chest pressure upon crouching or bending-forward (pronus angina). The factors that trigger pronus angina are not clear. We therefore investigated 28 patients with CAD and 26 normal subjects in the sitting, knee-chest, stooping, and squatting positions. Systolic and diastolic blood pressures were found to increase by 13.5 and 19.5 percent (p < 0.005) in the stooping position. In addition, left ventricular (LV) ejection time index (LVETI) also increased (p < 0.005). Despite the acute rise in aortic pressure, which is expected to lengthen the pre-ejection period index (PEPI), the latter shortened slightly in 10 of 14 (71 percent) patients tested, suggesting augmentation in contractile force during the isovolumic phase. Finally, left atrial size increased (p < 0.005) during the knee-chest maneuver, suggesting that the LV size also increases upon bending forward. The effect of stooping on blood pressure was similar in magnitude to that of squatting. It is concluded that the triggering factor for "pronus angina" in severe CAD may be explained as a combination of hemodynamic events which acutely increase myocardial oxygen requirements.