The analysis covers 150 patients subjected to open-heart surgery in the "St. Catherine" Hospital during the period January through April 1994. The postoperative complications are evaluated with a special emphasis on the risk factors involved. The timing of operation, cardiopulmonary bypass duration, and other predisposing factors are considered. In 105 patients (70 per cent) no complications are recorded in the early postoperative period (12-day postoperative hospitalization, and 30 days after discharge). In the remainder 45 patients (30 per cent), bacterial and abacterial complications develop in 23 cases (15.3 per cent) and 26 cases (17.3 per cent), respectively. Combined bacterial and abacterial complications are observed in 4 cases (2.7 per cent). The outcome of operation is significantly influenced by the timing of surgical intervention, duration of operation and cardiopulmonary bypass, intubation an chest re-exploration. The rest of the factors considered have no essential practical bearing on postoperative complications. In 17.7 per cent it is a matter of noninfectious complications where antibiotic treatment is unnecessary. Subfebrility as a single symptom after the sixth postoperative day is noted in many patients free of complications, and should be by no means considered as an indication for antibiotic therapy.