The aim of this study was to evaluate the effects of a diet supplemented with omega-3 polyunsaturated fatty acids (eicosapentaenoic and docosahexaenoic) and tocopherol, which are the base of a preparation "Tekom", on a composition of myocardial phospholipid fatty acids, as well as on the metabolism of eicosanoids, free radical processes and the contractility of isolated working heart in rats at ischemia/reperfusion. Added to the diet within 4 weeks, "Tekom" induced an increase in the content of omega-3 polyunsaturated fatty acids in membranes of cardiomyocytes, a decrease in vasoactive metabolites of arachidonic acid and limitation of free radical processes. "Tekom" inhibited cardiac arrhythmias in the isolated working hearts of rats and improved the cardiac pump function at ischemia/reperfusion.