Abstract: Objective:To investigate the protective effects and mechanisms of he ying an xin fangon myocardium injury caused by H₂O₂. Methods: Hydrogen peroxide (H₂O₂) was adopted to establish the rat embryonic cardiomyocytes oxidative stress insult model , and the experiment was divided into 5 groups: cardiomyocytes were incubated by H₂O₂ (200 μmol·L^-1) for 2h as model group, the non- H₂O₂ as control group, and the extraction of he ying an xin fang (500, 250, 125 mg·kg^-1) as therapeutic groups.
The cell viabilityby 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide (MTT), content of malondialdehyde (MDA) and activity of lactate dehydrogenase (LDH) were measured. Resulds: Cell viabilityby MTT: compared with control group, cell Viabilityby MTT was decreased significantly in H₂O₂ group (P< 0.01), while he ying an xin fang had no significant effect on cardiac myocytes of cell viability. Content of MDA: compared with that of H₂O₂ group, the content of MDA was decreased in he ying an xin fang groups significantly (P< 0.05). Content of LDH: compared with that of control group, the content of LDH was decreased in he ying an xin fang groups significantly (P< 0.05). Conclusion: He
ying an xin fang has significant protective effects on free radical injury induced by H₂O₂ in myocardium rats, and it may be related to the inhibition of lipid peroxidation.

Key words: He ying an xin fang, hydrogen peroxide (H₂O₂), myocardium, oxidative
stress