Reperfusion of the previously ischemic myocardium causes a burst of reactive oxygen species production that eventually leads to tissue damage. In the present study, the effect of long-term treatment with a red wine extract-containing antioxidant supplement (Super S.O.D) on myocardial ischemia/reperfusion (I/R) injury was examined in rats. To investigate the biochemical mechanism( s) involved in the cardioprotection, the effects of Super S.O.D treatment on myocardial mitochondrial antioxidant and structural parameters were also investigated. Long-term treatment with Super S.O.D (0.55 and 1.10 g/kg/day x 15) caused a dose-dependent protection against myocardial I/R injury in rats, as evidenced by the significant decrease in the extent of lactate dehydrogenase leakage. The cardioprotection was associated with increases in reduced glutathione level and antioxidant enzyme activities, including glutathione reductase, glutathione S-transferases and Mn-superoxide dismutase, and decreases in the extents of malodialdehyde production, Ca2+ loading and cytochrome c release, in non-ischemic and ischemic-reperfused rat hearts. The results indicated that long-term Super S.O.D treatment enhanced myocardial mitochondrial antioxidant status and structural integrity, thereby protecting against I/R injury. [ABSTRACT FROM AUTHOR]