Atrial pacing to the point of angina or up to a maximum rate of 166/min was carried out in 37 patients during coronary angiography. In 9 patients with normal coronary arteries both the right and left ventricular end-diastolic pressures fell remained steady with increasing heart rate. The same response was observed in 14 patients with angiographically proven coronary artery disease. In the remaining 14 patients with provencoronary artery disease the end-diastolic pressure in the left ventricle rose at the point when the patient experienced angina. In 10 of this latter group there was a simultaneous rise in the right ventricular end-diastolic pressure. In 4 patients the rise in end-distolic pressure was seen in the left ventricle only. The haemodynamic events in the right ventricle during angina appeared in most cases to mimic the events occurring in the left ventricle. There was no correlation between the angiographic findings and the changes in end-diastolic pressure in the two ventricles during angina.