Objective To research the attenuated effect and mechanism of different compositions of Sini Decoction（Counterflow Cold Decoction）according to their effects on rat hearts.Methods Totally 160SD rats were randomized into the normal group

Shengfu（Aconiti Radix Lateralis Cruda）group

Ganjiang（Zingiberis Rhizoma）group

Gancao（Glycyrrhizae Radix）group

Shengfu+ Ganjiang（3∶3）group

Shengfu+ Gancao（3∶2）group

Ganjiang+ Gancao（3∶2）group and Shengfu+ Ganjiang+ Gancao（3∶3∶2）group

with 20in each.The final concentration of medicinal extract in each group was 1g/ml and was administrated by injection into the duodenum at 2ml/kg based on animal body weight.The tracings of ECG lasted for 120minutes.The occurrence of frequent premature ventricular contractions after administration was taken as the cardiac toxicity criteria of Fuzi.The dose was reduced or increased at a ratio of 1∶0.8and one rat was used at each dose.The sequential form was introduced according to the former dose when arrhythmia occurred.The changes of ECG in 20rats were continuously observed.The cardiotoxic dose in each group was calculated according to the sequential form.Results The cardiotoxic dose was 6.25g/kg and arrhythmia time was（12.36±1.15）min in the Shengfu group.The cardiotoxic dose was4.19g/kg and arrhythmia time was（6.18±1.09）min in the Shengfu+ Ganjiang group.Comparing with the Shengfu group

the occurrence time of cardiac toxicity in the Shengfu+ Ganjiang group was significantly shortened（P<0.05）.There was no obvious cardiac toxicity in other groups.Conclusion The composition of Shengfupian and Ganjiang in Sini Decoction can increase the cardiac toxicity but Gancao can fight the cardiac toxicity of Ganjiang and Fuzi.