Due to their molecular configuration, most free radicals are highly reactive and can cause cell injury. The present review deals with the role of oxygen-free radicals (OFR) in the pathogenesis of the heart disease and reperfusion injury. Cellular protection against deleterious effects of OFR is organized at multiple levels. Regulation of the antioxidant capacity includes not only the maintenance of adequate levels of antioxidants but the localisation of antioxidant compounds and enzymes as well. Synthetic antioxidants may mimic biological defence mechanisms.