Reperfusion arrhythmias, a major cause of morbidity and mortality, can be prevented experimentally by preconditioning the heart with ischemia (“ischemic preconditioning” (IP)). While the mechanism responsible for this antiarrhythmic effect is unknown, a leading hypothesis is that IP depletes myocardial glycogen (G), thus limiting anaerobic glycolysis and lactic acidosis during subsequent ischemia. To test this hypothesis, we compared the incidence of sustained (>30 sec) VT or VF during reperfusion in 3 groups of rats (n=9 each) subjected to a 6-min left coronary occlusion. A control group (CON) received no pretreatment; a preconditioned group (IP) underwent three 2-min coronary occlusions at 5-min intervals prior to the 6-min occlusion; and a third group (GI+IP) received a 40-min infusion of glucose and insulin, to ‘load’ the heart with G, prior to IF’ Additional rats were used to determine the (G) (μmol/g) of the anterior myocardium just before (PRE-G) and just after (POST-G) the 6-min left coronary occlusion, and their difference (G-consumed).ResultsPRE-GPOST-GG-ConsumedVT orVFCON22±38±214±39/9*IP15±3*10±35±2*1/9GI+IP26±212±214±41/9*p<0,05 vs. other groupsThus IP rats had lower myocardial [G] prior to the 6–min coronary occlusion than CON rats, consequently consumed less G during the occlusion, and had a lower incidence of VT or VF on reperfusion. GI+IP rats were equally protected from arrhythmias however, despite pre-ischemic (G), and ischemic G-consumption, similar to CON rats. We conclude that neither the [G] of the myocardium prior to ischemia, nor the quantity of G consumed during ischemia, influence the incidence of reperfusion arrhythmias. This suggests the antiarrhythmic protection conferred by IP is not mediated by myocardial G depletion.