Objective To study the toxicity of herbicide,butachlor,to myocardium of Bufo bufo gargarizans. Methods One hundred and sixty Bufo bufo gargarizans were randomly divided into control group,paddy goup,5 times paddy group,10 times paddy group,forty in each group and the exposure was conducted in the experimental containers at the concentrations of 1,5,10 times of the application dosages( 5,10,30 ml/L) ,1/2 of the body of Bufo bufo gargarizans was immersed in the sulotion. After 3,6,9 days of exposure,electrocardiogram was recorded using calculator living creature signal analysis system and the structures of atrium muscle and ventricles muscle were observed with HE stain. Results The structure of myocardial cells of Bufo bufo gargarizans was damaged by butachlor with different levels. Pathological examination showed that the myocardial cells appeared necrosis in different degrees with the increasing doses of butachlor. Butachlor could affact the eletrocardiogram of Bufo bufo gargarizans with obvious dose-time-dependent manner,time-dependent manner was even dominant. Abnormal electrocardiogram was seen,P-R and Q-T changed. Conclusion Butachlor exposure can damage the structure and eletrocardiogram of myocardial cell in Bufo bufo gargarizans.