Background: Postoperative atrial fibrillation is common problem after cardiac surgeries. It is related to the rise in morbidity & hospital costs. Objective: The goal of the research was to assess the effectiveness of posterior pericardiotomy in reducing the incidence of postoperative pericardial effusion & consequently decreasing the related atrial fibrillation. Subjects and Methods: This randomized research included 100 patients scheduled for cardiac surgery in Kasr Al-