To characterize the effects of Ca2+ antagonists on the performance of the ischemic myocardium, we administered nifedipine and diltiazem to chloralose-anesthetized dogs with coronary artery occlusion and monitored segmental myocardial shortening in ischemic and nonischemic zones with implanted ultrasonic length gauges. Other dogs were treated with nitroglycerin or nitroprusside for comparison. Dosage of all drugs was adjusted to reduce mean aortic pressure by no more than 5 mmHg. Segmental shortening was expressed as percent of control value before occlusion. In control dogs (n = 8), shortening in ischemic zones 20 and 80 min after occlusion averaged -16 +/- 2% and -17 +/- 2%, indicating paradoxical elongation. With nifedipine (1 +/- 0.4 microgram . kg-1 . h-1; n = 8), shortening of ischemic segments before treatment did not differ from controls, but after 60 min of treatment was markedly improved, averaging 31 +/- 4% (P < 0.05). Diltiazem (10 +/- 2 microgram . kg-1 . h-1; n = 8) produced a similar improvement in shortening in ischemic zones. However, nitroglycerin (177 +/- 20 microgram . kg-1 . h-1; n = 8) and nitroprusside (43 +/- 10 microgram . kg-1 . h-1; n = 8) failed to improve shortening in ischemic regions. Thus, Ca2+ antagonists improved performance in ischemic zones, but nitroglycerin and nitroprusside did not.