Pervious biochemical and hemodynamic studies have highlighted the important role of epsilon PKC in cardioprotection during ischemic preconditioning. However, little is known about the electrophysiological consequences of epsilon PKC modulation in ischemic hearts. Membrane permeable peptide epsilon PKC selective activator and inhibitor were used to investigate the role of epsilon PKC modulation in reperfusion arrhythmias. Methods: Protein transduction domain from HIV-TAT was used as a carrier for peptide delivery into intact Langendorff perfused guinea pig hearts. Action potentials were imaged and mapped (124 sites) using optical techniques and surface ECG was continuously recorded. Hearts were exposed to 30 min stabilization period, 15 min of no-flow ischemia, followed by 20 min reperfusion. Peptides (0.5 mu M) were infused as follows: (a) control (vehicle-TAT peptide; TAT-scrambled psi epsilon ERACK peptide); (b) epsilon PKC agonist (TAT-psi epsilon RACK); (c) epsilon PKC antagonist (TAT-epsilon V1). Results: Hearts treated with epsilon PKC agonist psi epsilon RACK had reduced incidence of ventricular tachycardia (VT, 64%) and fibrillation (VF, 50%) compared to control (VT, 80%, P < 0.05) and (VF, 70%, P < 0.05). However, the highest incidence of VT (100%, P < 0.05) and VF (80%) occurred in hearts treated with epsilon PKC antagonist peptide epsilon V1 compared to control and to epsilon PKC agonist psi epsilon RACK. Interestingly, at 20 min reperfusion, 100% of hearts treated with epsilon PKC agonist psi epsilon RACK exhibited complete recovery of action potentials compared to 40% (P < 0.05) of hearts treated with epsilon PKC antagonist peptide, epsilon V1 and 65% (P < 0.5) of hearts in control. At 20 min reperfusion, maps of action potential duration from epsilon PKC agonist psi epsilon RACK showed minimal dispersion (48.2 +/- 9 ms) compared to exacerbated dispersion (115.4 +/- 42 ms, P < 0.05) in epsilon PKC antagonist and control (67 +/- 20 ms, P < 0.05). VT/VF and dispersion from hearts treated with scrambled agonist or antagonist peptides were similar to control. Conclusion: The results demonstrate that epsilon PKC activation by psi epsilon RACK peptide protects intact hearts from reperfusion arrhythmias and affords better recovery. On the other hand, inhibition of epsilon PKC increased the incidence of arrhythmias and worsened recovery compared to controls. The results carry significant therapeutic implications for the treatment of acute ischemic heart disease by preconditioning-mimicking agents. Published by Elsevier Inc.