Prophylactic use of an intraaortic balloon pump (IABP) prior to open-heart surgery in patients with impaired left ventricular function is still under debate. Patients with left ventricular ejection fraction (LVEF) < 40% were therefore compared according to time of IABP placement, viz. preoperative (n = 56), intraoperative (n = 40) or postoperative (n = 17), and also with patients who did not receive mechanical support despite LVEF < 40% (n = 78). The main indication for preoperative IABP insertion was severely impaired left ventricular function (80%), while patients with intraoperative or postoperative IABP placement mainly presented with low cardiac-output syndrome (70%/53%). Preoperative IABP was associated with a low mortality rate (8.9%), whereas patients with intraoperative or postoperative IABP placement had a high mortality risk and an increased catecholamine requirement. Of the patients scheduled for surgery without prophylactic IABP, 19% required intra- or postoperative insertion. Prophylactic placement of IABP thus reduced the mortality rate as well as the postoperative need for mechanical and catecholamine support. Need for intraoperative IABP insertion was associated with high mortality, whereas the outcome after postoperative IABP placement depended on the indication for the measure.