This study examined the role of Cu as a mediator of cardiac postischemic oxidative injury. Isolated rat hearts were subjected to 20 min of normothermic global ischemia, followed by 30 min of reperfusion; after 20 min of preischemic loading with Krebs-Henseleit buffer ± 20 or 30 µM zinc-bis-histidinate (Zn-His₂), 0.5 mM deferoxamine (DEF) or 42 µM neocuproine (NEO). Postischemic developed systolic pressure and rate-pressure product were highest and postischemic end-diastolic pressure was lowest in hearts treated with 20 or 30 µM Zn-His₂ and 0.5 mM DEF. Cu efflux was significantly increased by 225 and 290% (end of preischemic loading), and 325 and 375% (immediate postischemic period) of control basal rates in hearts treated with 30 µM Zn-His₂ and 0.5 mM DEF, respectively. NEO did not effect any of these parameters. By the end of ischemia, protein carbonyls were lowest in Zn-His₂-treated hearts and highest in DEF-treated hearts when compared with control hearts. The results of this study suggest that removal of redox-active Cu before ischemia has beneficial effects, indicating a mediatory role in postischemic cardiac oxidative injury.