In the heart sarcolemma and sarcoplasmic reticulum of rat there was significant decrease in cholesterol and phospholipid levels in isoproterenol treated rats. The membrane enzymes lipoprotein lipase and Ca-ATPase decreased due to myocardial necrosis. Lipid peroxide and xanthine oxidase were significantly enhanced, whereas superoxide dismutase was markedly decreased in ischemic heart produced by isoproterenol. Cytochrome P450, b5 and heme were found to be degraded in myocardial cell damage. Guggulsterone showed a marked protective effect on the cardiac enzymes and cyt P450 system against myocardial necrosis induced by isoproterenol.