To certify the protective effect of herbal medicine on myocardial damage against oxygen free radical-induced myocardiotoxicity, cytotoxicity was measured using by MTT assay, LDH activity and thiobarbituric acid reactive substances(TBARS) assay in the presence of Guaruhaebaekbaekju-tang(GHBT) extracts or single constituents of this prescription, Myocardial toxicity was evaluated in neonatal rat myocardiocytes in cultures. In the present study, xanthine oxidase/hypoxanthine (XO/HX) resulted in a decrease in cell viability, an increase in LDH activity in culture medium and lipid peroxidation in cultured myocardial cells, In the effect of GHBT extract, it showed the prevention from the XO/HX-induced cardiotoxicity such as the decrease of LDH activity and lipid peroxidation. In the protective effect of Fructus Trichosanthis (FT) and Bulbus Allii Macrostemi (BAM), all the extracts were significantly effective in the protection of XO/HX-induced cardiotoxocity in cultured myocardial cells. From these results, they show that XO/HX is cardiotoxic in cultured myocardial cells derived from neonatal rats, and it suggests that GHBT, FT and BAM extracts are positively effective in the blocking XO/HX-induced cardiotoxicity.