In order to elucidate toxic the mechanism of myocardial damage and the protective effect of herbal extract, Sophorae Radix(SR) against myocardiotoxicity, the cytotoxic effect of adriamycin and cardioprotective effect of SR were examined by MTT assay, LDH activity, heart beat rate and light microscopy after cultured myocardial cells derived from neonatal mouse were treated with various concentrations of adriamycin, an inducer of myocardiotoxicity. Adriamycin induced a decrease of cell viability, an increase in the amount of lactate dehydrogenase(LDH), and a decrease in the heart beat rate and a decrease in the number of cells, when administered to cultures myocardial cells in a dose-dependent manner. In cardioprotective effect of SR. SR showed the decrease of amount of LDH, and an increase of heart beating rate and cells in number on cultured myocardial cells damaged by adriamycin. From the above results, it is suggested that adriamycin shows toxic effect in cultured myocardial cells derived from a neonatal mouse, and herbal extract such as SR is very effective in the prevention of adriamycin-induced cardiotoxicity.