Endogenous glycogen stores are essential to maintain cell functions during myocardial ischemia.. Fasting and L-glutamate improve left ventricular function after an ischemic episode. We studied their effects on myocardial glycogen depletion during ischemia and on left ventricular function and glycogen resynthesis during reperfusion. We allocated 185 Wistar rats to 4 groups: 1) Control, 2) Fasting, 16-20 hours (Fast) 3) L-glutamate supplementation [100 mM] (Glt) or 4) Fasting + L-glutamate supplementation [100 mM]. n = 8-10 in each group. Hearts were mounted in an isolated perfused rat hearts model for 20 min stabilisation, 10/20/30 min ischemia and 60 min reperfusion. At each time point hearts were frozen in liquid nitrogen (-196 degrees C) within 2 seconds and myocardial contents of glycogen, lactate, alanine and glutamate were determined. Left ventricular pressure was measured continuously. Fasting and L-glutamate supplementation improved LV function after ischemia (Fast: p < 0.05, Glt: p < 0.01) and delayed myocardial glycogen depletion (Fast: p < 0.05, Glt: p < 0.01) compared to control. Decreased lactate accumulation and increased alanine content during ischemia were found in fasted (lactate: p < 0.05, alanine: p < 0.05) and L-glutamate supplemented (lactate: p < 0.01, alanine: p < 0.01) hearts compared to control. We did not find any additive effects of fasting and L-glutamate supplementation. In conclusion fasting and L-glutamate supplementation improve left ventricular function during reperfusion and delay myocardial glycogen depletion during ischemia. There were no additive effects of Fasting and L-glutamate supplementation. These finding suggest common metabolic pathways underlying the effects of L-glutamate supplementation and fasting.