AIM:To investigate the alteration of cardiac M3 receptor and its relationship with arrhythmias in various arrhythmic models.METHODS:Forty Wistar rats were randomly divided into 4 groups:control,aconitine,BaCl2 and ischemia.In the later three groups,arrhythmias were induced by treatment with aconitine,BaCl2 and coronary artery occlusion,respectively.The arrhythmias were recorded for 1 h.Western blotting was then used to detect M3 receptor contents.RESULTS:Arrhythmias were all induced in each group.In aconitine-induced arrhythmias,duration of arrhythmias and arrhythmia score were significantly increased than those in other two model groups.Western blotting showed that the expression of M3 receptor upregulated 2.3,1.4 and 1.3 folds respectively,more abundant in various arrhythmic groups than that in the normal control.Moreover,M3 receptor expression in aconitine group increased significantly than that in BaCl2 and ischemia group.The arrhythmias and M3 receptor protein expressions in myocytes were positively correlated.CONCLUSION:Arrhythmias upregulate the expression of cardiac M3 receptor.The upregulating levels of M3 receptor proteins diverge strikingly in different arrhythmic models.It is probably that the diversity of increase in M3 receptor is positive related to severity of ventricular arrhythmias.