To test the protective effect of herbal medicine on myocardial damage against oxygen free radical-induced myocardiotoxicity, cytotoxicity was examined using MTT, Beating rate and TSARS assay in the presence of water extract of Rhizoma Coptidis. Myocardial toxicity was evaluated in neonatal rat myocardiocytes in cultures. The results of these experiments were obtained as follows: Xanthine oxydase/hypoxanthine resulted in a decrease in viability, beating rate and in a increase in lipid peroxidation in Cultured myocardial cells. Rhizoma Coptidis water extract shows effects of protection from the cardiocyte toxicity induced by xanthine oxydase/hypoxanthine treatment such as increases in beating rate. Rhizoma Coptidis water extract shows effects of protection from the cardiocyte toxicity induced by xanthine oxydase/hypoxanthine treatment such as decreases in lipid peroxidation. These results show that xanthine oxydase/hypoxanthine elicits toxic effects. in cultured myocardial cells derived from neonatal rat, and suggest that water extract of Rhizoma Coptidis is very effective in the prevention of xanthine oxydase/hypoxanthine-induced cardiotoxicity.