Short intermittent periods of ischemia prior to a prolonged ischemia may protect the myocardium from ischemia-induced damage. This protective phenomenon has been termed ischemic preconditioning. The present study investigated the effects of multiple preconditioning cycles on arrhythmogenesis and contractile dysfunction. The possible role of protein kinase C (PKC) in ischemic preconditioning was investigated using the specific PKC inhibitor chelerythrine administered during various stages of the protocol. Findings show that 1 or 2 preconditioning cycles protect the heart against ischemia-induced ventricular fibrillation, while 3 or 4 cycles potentiate this arrhythmia. Also, ischemic preconditioning is more effective at protecting against ischemia-induced versus reperfusion-induced arrhythmias. Preconditioning does not appear to protect against contractile dysfunction during reperfusion, however, 2 and 3 preconditioning cycles decreased the degree of ischemic contracture. This study also shows that PKC inhibition during either the preconditioning ischemia or test ischemia abolishes the protection conferred by 1 preconditioning cycle. In contrast, PKC inhibition throughout the protocol did not alter the preconditioning response against arrhythmias. However, hearts exposed to chelerythrine throughout the protocol exhibited less shortening of MAPD than non-preconditioned hearts or hearts exposed to 1 cycle during the test ischemia. These results suggest that the effects of PKC inhibition on MAPD changes during ischemia do not correlate with its effects on arrhythmogenesis. (Abstract shortened by UMI.)