Prophylactic intraaortic balloon pump (IABP) support showed better outcomes in critical patients undergoing coronary revascularization compared with intraoperative or postoperative insertion. We conducted a prospective, randomized study to determine the optimal timing for preoperative IABP insertion in high-risk patients undergoing off-pump coronary artery revascularization.The study enrolled 230 consecutive high-risk patients (having a logistic European System for Cardiac Operative Risk Evaluation score of ≥10) undergoing off-pump coronary artery revascularization. They were randomized for preoperative IABP starting at 2 hours (2T, n = 115) or 12 hours (12T, n = 115). Clinical, biochemical, and hemodynamic results, and the need for inotropic drug support, were markers of outcome and compared between groups.Hospital mortality in group 12T was reduced by 60%, but the difference between groups was not statistically significant (hazard ratio, 0.4; 95% confidence interval, 0.1 to 1.5; p = 0.1). Twelve hours of preoperative IABP therapy reduced postoperative low output syndrome (hazard ratio, 0.4; 95% confidence interval, 0.1 to 0.9; p = 0.03) and biomarker leakage upper normal limit (hazard ratio, 0.3; 95% confidence interval, 0.1 to 0.7; p = 0.001). Postoperative left ventricular function was similar between the groups. Group 2T patients required higher inotropic support for a longer average duration and prolonged postoperative intensive care unit and hospital length of stay.Twelve hours preoperative IABP therapy improved treatment efficacy. Postoperative morbidity was reduced, but hospital mortality rate was not affected. The IABP-related complication rate was low and not related to the length of treatment.