To examine the cardiotoxicity of glucose oxidase(GO) in cultured myocardial cells, cardiotoxicity was measured by MTT assay. Myocardial cells were treated with 1～50 mU/ml GO for 5 hours. The cardioprotective effect of Benincasae Semen(BS) was measured by MTT assay in these cultrures. Cell viability was significantly decreased in dose- and time-dependently after myocardial cells were exposed to 30mU/ml GO for 5 hours. In the cardioprotective effect of BS on the cardiotoxicity induced by GO, BS prevented the cardiotoxicity induced by GO in these cultures. From these results, it suggests that GO had cytotoxic effect in cultured myocardial cells and herb extract, BS showed protective effect on GO-induced cardiotoxicity.