Background: Pericardial effusion (PE) develops very frequently after cardiac surgeries. It is one of the critical causes of cardiac tamponade developing after coronary artery bypass grafting (CABG). Posterior left pericardiotomy (PP) is a simple, easy, and efficient procedure in which the left pleural cavity is used to drain the pericardial area. Objectives: we aimed at 2 targets for our study. First, to detect the protectivity power of posterior pericardiotomy (PP) technique after CABG against the occurrence of early and late pericardial effusion (PE). Second, to detect the effect of posterior pericardiotomy (PP) procedure for preventing tamponade as a complication.  Patientsand Methods: A prospective randomized clinical trial was accomplished between November 2016 and November 2018 including 120 consecutive patients underwent CABG, in Elkasr Elaini Medical Center, Cardiovascular Surgery Department, Cairo University. Patients were allocated in two groups: 60 patients for each. Group 1 was a control one and Group 2 was a posterior pericardiotomy intervention group where a T-shaped incision was created from left inferior pulmonary vein to the diaphragm. Results: detected early PE in 13 patients (22%) in control group versus only in 3 patients (5 %) in PP group (p < 0.001). There was no late PE effusion or posterior tamponade noticed in the intervention group despite 6 (10 %) late PE developing (p < 0.001) and 7 (12%) posterior tamponade occurring in control group (p < 0.002). Conclusion: It could be concluded that posterior pericardiotomy (PP) has a beneficial effect in lowering the incidence of early and late pericardial effusions (PE) and cardiac tamponade in patients undergoing CABG surgery.