OBJECTIVE Postoperative nonlethal complications after open heart surgery are a serious clinical problem causing a considerable engagement of health workers, an augmented use of drugs, and prolonged operation incapac ity leading to prolonged hospital stay and increased expenses. The aim of the study was to establish whether there is any correlation between the level of expected operative risk and postoperative nonlethal complications. METHODS A consecutive series of 853 patients subjected to the open heart surgery were investigated, 622 (73%) males and 231 (27%) females. The average age of the patients was 57.2 +/- 9.9 (16-81) years. The patients were divided into 3 groups according to the additive EuroSCORE model: groups I, II and III with the expected operative risk of 0%-2%, 2%-5% and over 5%, respectively. The data were collected prospectively and analyzed retrospectively. Statistical methods of correlation and t-test were used. RESULTS A high degree of correlation between the operative risk level and frequency of postoperative nonlethal complications (R = 0.98) was found. The average rate of complications was 24% for the whole group of 853 patients. It accounted for 21%, 29% and 47% in the groups I, II and III, respectively. According to the expected operative risk level there was a statistically significant difference in respect of heart arrhythmias (p = 0.02), neurologic complications (p = 0.002), and pulmonary complications (p = 0.009). CONCLUSIONS Our results show a high degree of correlation between the expected level of operative risk according to the EuroSCORE model and the frequency of postoperative nonlethal complications. There is a statistically significant difference in respect to frequency of heart rhythm disturbances, pulmonary and neurological complications and expected operative mortality.