In 11 patients (9 men, 2 women) with angiographically confirmed coronary heart disease, hemodynamics, myocardial blood flow, oxygen consumption and lactate extraction were measured at rest before and after administration of 0.3 mg diltiazem per kg body weight. There was a prompt and sustained drop in mean systolic arterial pressure from 141 mm Hg to 127 mm Hg along with a reduction in total peripheral resistance. The filling pressure of the left ventricle remained constant following a post-injection rise lasting up to 5 minutes. A marked sustained drop in heart rate from 82/min to 73/min was registered. Concomitantly, stroke volume index rose from 39 to 49 ml/m2. Due to the decrease in load and frequency, contractility parameters dP/dt and dP/dt/P dropped slightly. Myocardial blood flow did not change. On the other hand, a decrease in the difference between arterial and coronary venous oxygen content indicated a coronary dilatory effect. Fifteen minutes after injection, myocardial oxygen consumption had dropped from 11.6 to 10 ml O2/min and 100 g of tissue. There was no substantial change in lactate extraction. Through a drop in peripheral arterial resistance and heart rate, diltiazem leads to a measurable decrease in myocardial oxygen consumption while the patient is still at rest. At the same time, there are indications of a coronary dilatory effect.