The effects of the new calcium channel blocking agent diltiazem were evaluated in 11 patients with stable angina pectoris and confirmed obstructive coronary artery disease at rest and during rapid atrial pacing. Symptomatic, metabolic, coronary, and systemic haemodynamic indices were monitored at rest and during pacing induced ischaemia. At rest, after the administration of intravenous diltiazem, potent vasodilator effects were observed with a significant fall in mean blood pressure and an increase in cardiac index. Importantly, however, the systemic vasodilator effect of diltiazem was associated with no significant increase in heart rate. During pacing there was similar decrease in mean blood pressure after diltiazem, and mean pacing time to angina increased significantly. Three patients did not develop angina on repeat pacing. Coupled with an improved pacing time to angina there was a significant improvement in myocardial lactate extraction during pacing, changing from lactate production to lactate extraction after diltiazem. This study confirms the antianginal effects of diltiazem and suggests that this agent may have advantages in the management of angina pectoris. The results suggest that diltiazem may exert its beneficial effect not only by reducing afterload reduction but also by a direct metabolic effect on the myocardium.