Coronary artery bypass grafting remains the standard treatment for patients with extensive coronary artery disease. Coronary surgery without use of cardiopulmonary bypass avoids the deleterious systemic inflammatory effects of the extracorporeal circuit. However there is an ongoing debate surrounding the clinical outcomes after on-pump versus off-pump coronary artery bypass (ONCAB versus OPCAB) surgery. The current review is based on evidence from randomized controlled trials (RCTs) and metaanalyses of randomized studies. It focuses on operative mortality, mid-and long-term survival, graft patency, completeness of revascularisation, neurologic and neurophysiologic outcomes, perioperative complications and outcomes in the high risk groups. Early and late survival rates for both OPCAB and ONCAB grafting are similar. Some studies suggest early poorer vein graft patency with off-pump when compared with onpump, comparable midterm arterial conduit patency with no difference in long term venous and arterial graft patency. A recent, pooled analysis of randomised trials shows a reduction in stroke rates with use offpump techniques. Furthermore, OPCAB grafting seems to reduce postoperative renal dysfunction, bleeding, transfusion requirement and respiratory complications while perioperative myocardial infarction rates are similar to ONCAB grafting. The high risk patient groups seem to benefit from off-pump coronary surgery. Developed about 40 decades ago (5-7), OPCAB reached a plateau in Europe, accounting for nearly 15-20% of all coronary operations, while in Asia 60-100% of patients are offered coronary artery bypass grafting (2). A retrospective analysis of the Society of Thoracic Surgeons Adult Cardiac Surgery Database in USA revealed a decline in off-pump operations, currently being used in fewer than one out of five patients (8). The current review focuses on the main outcomes of on-pump coronary artery bypass (ONCAB) grafting versus OPCAB from randomized controlled trials (RCTs) (i.e., level I evidence). The main criticism of RCTs in this area, is the under powering because of recruitment of low risk patients but also because of the low mortality and morbidity of coronary artery bypass grafting that would require very large sample populations to detect a difference (4). Therefore, we will also be reviewing pooled data from recent, updated meta-analyses of randomized trials only. We selected in our review large sample size RCTs or large meta-analyses of RCTs to discuss the hard end-point outcomes but smaller trials were also included to discuss other outcomes. Operative mortalityThe majority of the large RCTs to date failed to show a difference in early mortality between off-pump and on-pump surgery (1,3,9-13). One small sample size RCT by Fattouch et al. showed a reduced mortality in patients with ST elevation undergoing urgent/emergent off-pump coronary surgery compared to on-pump surgery (14). Deppe et al. in meta-analysis of RCTs on almost 16,900 patients found no difference in 30-day mortality. Kow...