Continuous warm blood cardioplegia is often temporarily interrupted during coronary artery operations to provide the surgeon with a bloodless operating field. To determine the effects of intermittent warm ischemia on myocardial recovery, we randomized 15 adult mongrel dogs to receive either multidose cold or warm blood cardioplegia during a 90-minute arrest. Myocardial metabolic and functional recovery was assessed before clamping of the aorta and after 30 and 60 minutes of reperfusion. Systolic function was well preserved, whereas diastolic function decreased slightly in both groups after arrest. Myocardial oxygen consumption increased during reperfusion after cold heart protection but was unchanged after warm blood cardioplegia. High-energy phosphates decreased significantly in both groups during reperfusion. Two conclusions were reached. (1) Myocardial functional recovery was well preserved, whereas metabolic recovery was impaired after either technique of myocardial preservation. (2) Preserved functional recovery after multidose warm blood cardioplegia suggests that repetitive episodes of ischemia may condition the myocardium, thus preventing injury during prolonged aortic cross-clamping.