Objectives: Postoperative atrial fibrillation (POAF) is a common complication after cardiac surgery and might be avoided with amiodarone prophylaxis. We investigated the long-term effect of prophylactic amiodarone, in patients undergoing isolated, elective coronary artery bypass grafting (CABG), as well as the long-term prognosis of patients with POAF. Methods: We retrospectively analysed patients included in the randomized, control trial RASCABG allocated to either placebo or amiodarone as POAF prophylaxis. Several outcomes were evaluated using national databases. Patients were stratified and compared by prophylactic groups and rhythm. Cox proportional hazard analysis was used for multivariable analysis. Kaplan-Meier survival curves were constructed to assess the probability of survival and cumulative incidence curves. Results: Prophylactic amiodarone was not related to long-term side effects in comparison to placebo. Patients who developed POAF, were more likely to develop late AF, and had a worse overall survival. There was no difference in the overall survival between prophylactic groups. In the competing risk analysis, amiodarone and POAF was not associated with an increased risk of readmission, but POAF was associated with an increased risk of late AF HR 2.28 [95% CI 1.15; 4.55]. In the multivariable analysis, amiodarone was not associated with late AF, readmission or long-term mortality. Further, no association was found between POAF and late AF, readmission or long-term mortality. Conclusion: Amiodarone is a safe drug for the prevention of POAF in the RASCABG-setting. POAF is related to long-term worse prognosis regarding late AF and mortality.