Oxygen-derived free radicals are highly reactive molecules characterized by the presence of an unpaired electron in one of its outer orbitals. They have been found responsible for some pathologic phenomenons which in the field of cardiology, occurs during tissue reperfusion of a previously ischemic area. Ischemia predisposes an outburst in the production of these molecules upon the reintroduction of oxygen during reperfusion. Animal experimental models have been designed to reduce the damages induced by free radicals using various pharmacologic agents. It is probable that these agents may form a part of the conventional treatment of certain cardiac pathologies in the future.