To certify the protective effect of herbal medicine against oxygen free radical-induced myocardiotoxicity, cytotoxicity was measured using LDH activity and TBARS assay in the presence of Jisilhaebaekgyejitang(JHGT) extracts or single constituents of this prescription, In the present study, xanthine oxidase/hypoxanthine (XO/HX) resulted in a cell damage such as increases in LDH activity in culture medium and lipid peroxidation in cultured myocardial cells. In the effect of JHGT extract and its single constituents, which are Fructus Ponciri Seu Aurantii Immaturus (FPSAI), Cortex Magnoliae Officinalis (CMO), Bulbus Allii Macrostemi (BAM), Ramulus Cinnamomi (RC) and Fructus Trichosanthis (FT), they showed the prevention from the XO/HX-induced cardiotoxicity by the decrease of LDH activity and lipid peroxidation. From these results, they show that XO/HX is cardiotoxic in cultured myocardial cells derived from neonatal rat, and it suggests that JHGT, FPSAI, PT, CMO, BAM, RC and FT extracts are positively effective in the blocking in XO/HX-induced cardiotoxicity.