Background: In the majority of patients with pacemakers, when AF develops it is “clinically silent” both because traditional symptoms are absent and because atrial rhythm diagnosis on a single-lead ECG may be difficult. Objective: To assess the prevalence of atrial fibrillation in patients with high degree heart block after implantation of VVI(R) mode pacemaker. Patients and methods: This study included 122 patients attending Benha University Hospitals and Nasr City Insurance Hospital pacemaker clinics for follow up to assess the incidence of AF.(all patients were not in AF at time of pacemaker implantation), Patients were divided according to their atrial rhythm at the time of follow up into two groups : Group I included(89) patients with sinus rhythm at the time of follow up, Group II included(33) patients with AF at the time of follow up. All patients were suspected to full clinical data, resting twelve electrocardiogram and transthoracic Echocardiographic study to detect LA dimension, LV end diastolic dimension, LV end systolic dimension, LV EF and presence of MR. Results: We found that 33 (27.5%) of 122 Consecutive patients attending for routine follow up have AF , there were 37(30.3%) patients with IHD, 42(34.4%) patients with hypertension, 18(14.7%) patients with DM, there was no statistically significant relationship between the two groups, the longer duration of pacing the more incidence of atrial fibrillation(in the pacing period above 5 years p=0.001). The mean value of left atrial dimensions in group I was 36.81 ± 4.52 versus 43.73±3.63 in group II and there was highly significant P value=0.001.The presence of mitral regurge is highly statistically increased in group II .The only 3 (9 %) patients who had AF were anticoagulated , and 25(75.7%) out of 33 patients met the high risk criteria for thromboembolism. Conclusion: The prevalence of AF were 27.5% , there is a significant relationship between occurrence of AF after VVI(R) pacemaker and MR, LA dimension and duration of pacing, Only 3(9%) of the patients who had AF were anticoagulated