In 10 patients undergoing percutaneous transluminal coronary angioplasty of the left anterior descending coronary artery (LAD), the clinical, electrocardiographic and hemodynamic effects of acute intravenous calcium channel antagonism with nicardipine (2 mg over 1 minute, followed by a constant infusion of 25 to 50 micrograms/min) were assessed during temporary LAD occlusion. Onset of myocardial ischemia during coronary occlusion was prevented or delayed after administration of nicardipine in 7 of the 10 patients. During infusion of nicardipine and during LAD occlusion, residual great cardiac vein blood flow increased in 9 of 10 patients compared with residual flow during occlusion before nicardipine (10%, p less than 0.05). Nicardipine also decreased mean aortic pressure, but was associated with a reflex-mediated increase in heart rate. Overall, the double product, an index of global myocardial oxygen demand, decreased 7% (p less than 0.05). Thus, nicardipine usually diminished ischemia induced by acute transient coronary occlusion by increasing collateral flow while oxygen demand decreased.