During the years 1988-1991 6319 patients underwent cardiac surgical procedures in Denmark. In 183 patients (2.9%) with left ventricular failure intra-aortic balloon counterpulsation (IABP) was used. Four percent of the IABP were placed preoperatively, 86% intraoperatively and 10% postoperatively. Severe complications occurred in 16 patients (8.7%) and were mainly vascular due to limb ischemia. The incidence of complications was independent of the duration of balloon pumping. Sixty percent of the patients were weaned from IABP. The 30-day mortality rate was 54%. During the observation period we found a gradual decrease in the use of IABP as well as a reduction in mortality.