Iron catalysis is involved in the generation of the highly cytotoxic hydroxyl radical and in the chain reactions of subsequent lipid peroxidation that lead to irreversible membrane damage. Assuming that ischemically stored heart transplants may incur free radical injury at the time of reoxygenation, we assessed the effects of the iron chelator deferoxamine in 70 isolated isovolumic buffer-perfused rat hearts subjected to the following protocol: cardioplegic arrest; cold (2° C) storage for 5; hours global ischemia at 15≤ C for 1 hour, intended to simulate the implantation procedure; and normothermic reperfusion for 1 additional hour. During poststorage ischemic arrest, the following techniques of myocardial protection were evaluated: hypothermia alone high-pressure (60 cm H2O) cardioplegia given at 0.30, and 55 minutes of arrest low-pressure (30 cm H2O) cardioplegia given at 0 and 55 minutes of arrest; and low-pressure (30 cm H2O) cardioplegia only given at 55 minutes of arrest. Treated hearts had deferoxamine (6 μmol) added to the cardioplegic solution used throughout the experimental time course. Further, in the treated group subjected to the protocol of single cardioplegic delivery at end ischemia, deferoxamine was given both in the cardioplegic reperfusate and in the Krebs buffer over the 15 initial minutes of reflow. Based on comparisons of postreperfusion ventricular pressure development, maximal rate of rise of ventricular pressure, left ventricular compliance, and coronary flow, the best myocardial protection was afforded by deferoxamine given as an additive to single-dose cardioplegic solution at the end of arrest and to the reperfusate during the initial phase of reoxygenation. As the drug has no inotropic effect, its protective action is most likely related to a decrease in catalytic iron available for free radical production and lipid peroxidation. These results support the hypothesis that oxidative damage may contribute to donor heart failure and demonstrate that this form of damage can be efficiently acted upon by iron chelation. The clinical relevance of these data stems from the fact that deferoxamine is available for human use and might become an effective means of improving donor heart preservation in the setting of clinical heart transplantation.