The dietary polyunsaturated fatty acids are well known to promote the cardiac output and to protect the myocardium against arrhythmias. The exogenous glucose is generally considered as a protective agent against arrhythmias resulting from ischemia and reperfusion. But the effects of dietary fats, which also influence arrhythmias, on this beneficial effect of glucose has not been yet considered. We have studied the effects of a 7 days diet with or without polyunsaturated fatty acids on the cardiac performance and arrhythmias of isolated rat hearts, perfused with saline containing either glucose 5.5 mM or 11 mM. Acute regional ischemia was produced by ligature of the left main coronary artery with subsequent release to achieve reperfusion for some hearts. Previously, our results showed that the dietary polyunsaturated fatty acids led to an enhancement of the cardiac performance and to a decreased susceptibility to arrhythmias. The present data showed that the protective action of the exogenous glucose appeared to be dependent of the dietary lipid profile. Dietary polyunsaturated fatty acids increase cardiac performance under ischemia and decrease ventricular arrhythmias' occurrence under ischemia and on reperfusion. It might be related to endogenous substrate utilization and exogenous glucose availability which was influenced by the coronary flow.