The goal of this study was to investigate whether sub-chronic anti-oxidant treatment with ascorbic acid (Vit C) is able to protect the heart against myocardial infarction. The effects of Vit C treatment on the histopatological changes and immunohistochemistry for p53, COX-2 and iNOS were evaluated in rats submitted to acute myocardial infarction induced by isoproterenol (ISO). Male Wistar rats (n = 32) were divided into four groups: group 1, control; group 2, ISO treated; group 3, Vit C treated; group 4, ISO + Vit C treated. An amount of 150 mg/kg of isoproterenol was administered for two consecutive days. The rats were treated with Vit C once a day (150 mg/kg, orally) for seven consecutive days. In the day 5 and 6 the rats from group ISO + Vit C were submitted to acute administration of ISO third minutes after Vit C treatment. The results pointed out that treatment with Vit C showed mild degenerative changes of myocardial tissue in ISO group. Also, the antioxidant was able to decrease the iNOS expression in rats treated with Vit C. Taken together, our results suggest that chronic Vit C administration was able to prevent the myocardial infarction induced by ISO as a result of iNOS downregulation. Certainly, this finding offers new insights into the mechanisms underlying the relation between oxidative stress and cardiac mortality after myocardial infarction.