Objective To investigate the influence to atrial fibrillation occurs of long -term use of trimetazi-dine in treatment of dilated cardiomyopathy.Methods 90 cases with dilated cardiomyopathy (DCM)were averagely divided into the observation group and the control group according to a random number table,45 cases in each group. The patients of the control group were treated with conventional anti -heart failure according to their heart function, the patients of the observation group were given oral trimetazidine on the bases of conventional anti -heart failure. After follow -up six months,the left ventricular ejection fraction (LVEF),left ventricular end diastolic diameter (LVEDD),improve heart function,as well as the incidence of atrial fibrillation after treatment of two groups were compared.Results The rate of occurrence after treatment of the observation group atrial fibrillation of was 2.27%, which was significantly lower than 11.11% of the control group,the difference was statistically significant(χ2 =10.74,P <0.05).The left ventricular end diastolic diameter (LVEDD)after treatment of the observation group was (52 ±9)mm,which was significantly lower than (63 ±11)mm of the control group,the difference was statistically sig-nificant(t =6.83,P <0.05);The left ventricular ejection fraction (LVEF)of the observation group was (54 ±7)%, which was significantly higher than (41 ±6)% of the control group,the difference was statistically significant(t =8.72,P <0.05).Conclusion Dilated cardiomyopathy patients taken long -term trimetazidine,can greatly reduce the incidence of atrial fibrillation.