Introduction: Atrial Fibrillation (AF) is the most common arrhythmia found in patients scheduled to undergo mitral valve replacement surgery. Various ablation therapies or pharmacological agents are used to prevent AF. Although ablation therapies can be effective in some patients, these therapies may not be appropriate for all patients, and pharmacological treatments will continue to have an important place in the prevention of AF and maintenance of normal sinus rhythm. Aim: The aim of our study was to evaluate the effect of single dose intravenous amiodarone on post bypass cardiac rhythm in patients with pre-existing atrial fibrillation undergoing valvular surgery and study if Amiodarone (IV) given prior to cross-clamp release is helpful in preventing the recurrence of Atrial fibrillation. Materials & Methods: In this prospective randomized, double blind controlled study, patients with pre-existing atrial fibrillation undergoing mitral valve replacement (MVR) were divided into two groups, Group A receiving prophylactic intravenous amiodarone 3mg/kg and their post bypass rhythms were compared with group B (control group). If NSR was established, it’s maintenance or recurrence of AF was watched for. If NSR was not established, the need for cardioversion, amount of energy needed for defibrillation and the response to defibrillation was compared in both the groups. Results: There was statistically significant difference in the number of patients who reverted to normal sinus rhythm after aortic cross clamp removal when given IV Amiodarone prophylactic ally as compared to the control group. There was statistically significant difference in the number of patients who needed cardioversion. In the control group, 39 patients (54.9%) required cardioversion whereas only 21 patients (29.5%) who received IV Amiodarone group required cardioversion. The duration of ICU stay and duration of hospital stay was comparable between the groups. There was no significant difference in the incidence of complications between Group A and Group B. Conclusion: Amiodarone given as a single intravenous dose in patients with pre-existing atrial fibrillation undergoing valvular surgery, prior to cardiopulmonary bypass was found to be effective in reducing the incidence of atrial fibrillation after aortic cross clamp release. It decreased the requirement of cardioversion after the release of aortic cross clamp. [ABSTRACT FROM AUTHOR]