Purpose: Ischemic heart disease carries an increased risk of malignant ventricular tachycardia, (VT), fibrillation (VF), and sudden cardiac death. Protein kinase C (PKC) epsilon activation has been shown to improve the hemodynamics in hearts subjected to ischemia/ reperfusion. However, very little is known about the role of epsilon PKC in reperfusion arrhythmias. Here we show that epsilon PKC activation is anti-arrhythmic and its inhibition is pro-arrhythmic. Method: Langendorff-perfused isolated hearts from epsilon PKC agonist (ePKC activation), antagonist (epsilon PKC inhibition) transgenic (TG), and wild-type control mice were subjected to 30 min stabilization period, 10 min global ischemia, and 30 min reperfusion. Action potentials (APs) and calcium transients (CaiT) were recorded simultaneously at 37 degrees C using optical mapping techniques. The incidence of VT and VF was assessed during reperfusion. Results: No VT/VF was seen in any group during the stabilization period in which hearts were perfused with Tyrode's solution. Upon reperfusion, 3 out of the 16 (19%) wild-type mice developed VT but no VF. In epsilon PKC antagonist group, in which epsilon PKC activity was downregulated, 10 out of 13 (76.9%) TG mice developed VT, of which six (46.2%) degenerated into sustained VF upon reperfusion. Interestingly, in epsilon PKC agonist mice, in which the activity of epsilon PKC was upregulated, no VF was observed and only 1 out of 12 mice showed only transient VT during reperfusion. During ischemia and reperfusion, CaiT decay was exceedingly slower in the antagonist mice compared to the other two groups. Conclusion: Moderate in vivo activation of epsilon PKC exerts beneficial antiarrhythmic effect vis-a-vis the lethal reperfusion arrhythmias. Abnormal CaiT decay may, in part, contribute to the high incidence of reperfusion arrhythimas in the antagonist mice. These findings have important implications for the development of PKC isozyme targeted therapeutics and subsequently for the treatment of ischemic heart diseases. (c) 2006 Elsevier Inc. All rights reserved.