The optimal use of prophylactic intra-aortic balloon pump (IABP) to prevent postcardiotomy low cardiac output syndrome (LCOS) is still debated and poorly defined. The aim of this study was to evaluate whether prophylactic IABP reduces the rate of postcardiotomy LCOS and improves the early outcome in hemodynamically stable, high-risk patients undergoing coronary artery bypass grafting (CABG). From May 2004 to August 2007, 141 consecutive risk patients underwent CABG. Of these 38 (27%) received prophylactic IABP. The remaining 103 patients underwent operation without preoperative insertion of the device. Prophylactic IABP patients were more likely to be younger (P<0.0001), had a recent myocardial infarction (P<0.0001), lower ejection fraction (P=0.006), and higher New York Heart Association (NYHA) functional class (P=0.05). After risk-adjusting for propensity score, prophylactic IABP patients had a lower incidence of postcardiotomy LCOS (adjusted OR 0.07, P=0.006), postoperative myocardial infarction (adjusted OR 0.04, P=0.04), a shorter length of hospital stay (10.4+/-0.8 vs. 12.2+/-0.6 days, P<0.0001) than those who did not receive IABP. This study shows that prophylactic IABP treatment for hemodynamically stable high-risk patients undergoing CABG may improve postoperative course reducing postcardiotomy LCOS, postoperative myocardial infarction and length of hospital stay.