Diastolic pressure-volume relations of the left ventricle were studied in 7 dogs during partial and complete coronary occlusion. The pericardium was widely opened and the dogs were instrumented with a left ventricular micromanometer, cuff occluders around the left circumflex coronary artery and inferior vena cava, and ultrasonic crystals to measure control and ischemic wall thickness as well as both left ventricular long and short axes. Measurements were performed at rest and after 2 minutes of partial and complete coronary occlusion. The first experiment was performed without caval occlusion and a second experiment was carried out a few days later with caval occlusion. During partial coronary occlusion, no shift of the diastolic pressure-volume relationship was observed. However, during complete coronary occlusion the pressure-volume curve was shifted significantly upwards but no shift was observed when occlusion of the inferior vena cava was carried out. These findings suggest that the shift of the diastolic pressure-volume relationship during coronary occlusions (1) depends on the extent of myocardial ischemia and (2) is related to ventricular interaction since the shift was prevented by caval occlusion.