OBJECTIVE：To study the toxicity mechanism of yunacotine-induced arrhythmia in rats. METHODS ：Totally 32 rats were randomly divided by random number table method into normal control group ，yunacotine low-dose and high-dose groups （0.09，0.14 mg/kg），aconitine group （positive control ，0.88 mg/kg），with 8 rats in each group. Administration groups were given the corresponding drugs once a day ，and normal control group was given the constant volume of normal saline ，for consecutive 7 d. After last intragastric administration ，the changes of electrocardiogram （ECG） were observed. The contents of adenosine triphosphate（ATP）in myocardial tissue and Ca 2+ in myocardial cells ，the activities of Na +-K+-ATPase and Ca 2+-Mg2+-ATPase as well as the protein expression of ranolidine receptor 2（RyR2）and Ca 2+-ATPase（SERCA2）in myocardial tissue were determined. RESULTS：Compared with normal control group ，time limit of QRS wave and QTc intervals of rats were prolonged significantly in yunaconitine low-dose group （P＜0.01）. The content of Ca 2 + in myocardial cells ， the ATP contents ， the activities of Ca2+-Mg2+-ATPase and Na +-K+-ATPase as well as the protein expression of SERCA 2 in myocardial tissue were reduced significantly （P＜0.05 or P＜0.01）. The heart rate of rats in yunaconitine high-dose group and aconitine group were increased significantly （P＜ 0.05 or P＜0.01），and time limit of QRS wave and QTc intervals were significantly prolonged （P＜0.01）；the content of Ca 2+ in myocardial cells was increased significantly （P＜0.01）；ATP content ，the activities of Ca 2+-Mg2+-ATPase and Na +-K+-ATPase，and protein expression of RyR 2 and SERCA 2 in myocardial tissue were decreased significantly （P＜0.01）. CONCLUSIONS ： Yunaconitine can induce arrhythmia in rats ，the mechanism of which may be associated with Ca 2+ overload that resulted from reducing the activities of Na +-K+-ATPase and Ca 2+-Mg2+-ATPase and down-regulating the expression of related calcium transporter RyR2 and SERCA 2.