The hydroxyl radical is one of the most damaging oxygen metabolites that are thought to be produced during ischemia and reperfusion of cardiac tissue. Therefore, we used the isolated, isovolumetric, buffer-perfused rat heart preparation of cardioplegic arrest to assess the effects of interventions targeted at inhibiting production of the hydroxyl radical by decreasing either the availability of one of its precursors (hydrogen peroxide) or that of the metal catalyst (ferric iron) involved in the radical formation. Sixty hearts were studied and, except for nonischemic controls, were subjected to 3 hr of hypothermic (15 degrees to 18 degrees C) cardioplegic arrest, followed by 45 min of reperfusion. The following interventions were tested: pretreatment with peroxidase, a scavenger of hydrogen peroxide, pretreatment with a combination of peroxidase and the iron chelator deferoxamine, pretreatment with peroxidase followed by supplementation of the cardioplegic solution with deferoxamine, and supplementation of the cardioplegic solution with deferoxamine without preischemic enzymatic treatment. Based on comparisons of postreperfusion pressure development, maximal ventricular dP/dt, left ventricular compliance, and coronary flow, deferoxamine-containing cardioplegic solution alone afforded the best myocardial protection. This may be due to the ability of deferoxamine to act both as an iron chelator and as a direct scavenger of superoxide anion, an activated oxygen species that participates in hydroxyl radical formation. This study confirms that an important component of the cardiac damage sustained during global ischemia and reperfusion may involve injury caused by the hydroxyl radical. Furthermore, our results point out the potential therapeutic usefulness of deferoxamine in the context of cardioplegic protection during open-heart procedures.