This study was designed to evaluate the role of heart rate, aortic pressure, and aortic flow in the development of coronary insufficiency following acute coronary stenosis. In dogs, each of these parameters was controlled at a predetermined level while the left anterior descending coronary artery was constricted with a small screw clamp. The critical coronary pressure (CCP), i.e. the pressure below which a rise of left atrial pressure could be detected, was determined at various levels of hemodynamic load. Increases in aortic pressure, elevation of the heart rate and an increase in aortic flow rate were all associated with an elevation of the CCP and an increase in tension-time index (TTI). The changes in CCP were most striking when TTI was increased by aortic flow rate change. These findings suggest that with high aortic pressure, further constriction of coronary artery is required to precipitate coronary insufficiency, that the level of pacing required to induce coronary insufficiency is a useful index in assessing the degree of coronary stenosis, and that an augmentation of aortic flow rate is an important factor in the initiation of coronary insufficiency.