OBJECTIVE The aim of this prospective study was to demonstrate the effectiveness of posterior pericardiotomy in reducing the incidence pericardial effusions and consequently reducing the related supraventricular tachyarrhythmias and development of delayed posterior cardiac effusions. METHODS This prospective randomized study was carried out in 150 patients undergoing coronary artery bypass grafting in Bayindir Hospital Department of Cardiovascular Surgery between April 2000 and October 2001. One hundred and fifty patients were divided into two groups; each group included 75 patients. A 4-cm longitudinal incision was made parallel and posterior to the left phrenic nerve, extending from the left inferior pulmonary vein to the diaphragm in posterior pericardiotomy group (group I). Posterior pericardiotomy was not performed in conventional treatment group (group II). RESULTS Atrial fibrillation was developed in seven patients (9.3%) in group I and in 24 patients (32%) in group II (P<0.001). Atrial flutter and other supraventricular tachyarrhythmia (SVT) prevalence was not statistically significant. Early pericardial effusion was developed 42.6% (32/75) and 10.6% (8/75), respectively, in group II and group I (P<0.0001), but no late pericardial effusion developed in group I despite seven (9.3%) late pericardial effusions developing in group II (P<0.013). CONCLUSIONS Posterior pericardiotomy is a simple, safe and effective technique for reducing not only the prevalence of early pericardial effusion and related atrial fibrillation but also delayed posterior pericardial effusion and tamponade.