Antioxidant activity of ethanolic extract of fruits of Terminalia chebula (500 mg/kg body wt, orally for 30 days) against isoproterenol-induced oxidative stress was investigated in rats. The levels of serum lipid peroxides, iron, ascorbic acid, vitamin E, plasma iron-binding capacity, and the activities of ceruloplasmin and glutathione were assayed, in addition to the activities of the antioxidant enzymes--glutathione peroxidase, glutathione reductase, glutathione-S-transferase, superoxide dismutase and catalase in the heart tissue. Administration of isoproterenol increased the levels of lipid peroxides and iron, with corresponding decrease in the activities of the enzymic and non-enzymic antioxidants. The pre-treatment with ethanolic extract of fruits significantly prevented the alterations induced by isoproterenol, and maintained a near normal antioxidant status. Results suggest that the cardioprotective effect of T. chebula fruit may partly be attributed to its antioxidant properties.