Mechanisms of burn related cardiac dysfunction may involve defects in mitochondria. This study determined: (1) whether burn injury alters myocardial mitochondrial integrity and function; and (2) whether an antioxidant vitamin therapy prevented changes in cardiac mitochondrial function after burn. Sprague Dawley rats were given a 3° burn over 40% TBSA and fluid resuscitated. Antioxidant vitamins or vehicle were given to sham and burn rats. Mitochondrial and cytosolic fractions were prepared from heart tissues at several times post burn. In mitochondria, lipid peroxidation was measured to assess oxidative stress, mitochondrial outer membrane damage and cytochrome C translocation were determined to estimate mitochondrial integrity, and activities of SOD and GPx were examined to evaluate mitochondrial antioxidant defense. Cardiac function was measured by Langendorff model in sham and burn rats given either vitamins or vehicle. Results: In 24 hrs post burn, mitochondrial outer membrane damage was progressively increased to ~50% and cytosolic cytochrome C gradually accumulated to ~3 times more than that measured in shams, indicating impaired mitochondrial integrity. Maximal decrease of mitochondrial SOD activity occurred 8 hrs post burn (~63.5% of shams) whereas maximal decrease in GPx activity persisted 2-24 hr post burn (~60% of shams). In burn animals, lipid peroxidation in cardiac mitochondria increased 30-50%, suggesting burn induced oxidative stress. Antioxidant vitamin therapy prevented burn-related loss of membrane integrity and antioxidant defense in myocardial mitochondria, and prevented cardiac dysfunction. These data suggest that burn mediated mitochondrial dysfunction and loss of ROS defense may play a role in post burn cardiac dysfunction.