The purpose of this study was to examine the early and late results of CABG in patients with left ventricular ejection fraction (LVEF) lower than 40%. This study comprised 128 patients (114 male and 14 female) at age from 41 to 75 years (mean 58.3 +/- 7.9). Before operation 115 patients (89.8%) were in CCS class III or IV. Before operation in all patients coronary arteriography with left-sided ventriculography were performed. In 12 patients myocardial perfusion in SPECT with Tc-99m-MIBI was assessed. Perioperative mortality in whole group was 12.5% (16 patients). The lowest (9.2%) was in subgroup with LVEF from 0.31 to 0.4 and the highest (27.3%) in patients with LVEF below 0.2. In 8 patients death was caused by low cardiac output, in 4 by ventricular fibrillation, in the others by renal failure or cerebral stroke (2 patients in each). In 45 patients (35.2%) postoperative low cardiac output was observed. In 41 patients was treated with the use of intraaortic balloon pumping (IABP). Twenty seven (65.9%) patients with IABP survived. During follow-up died 5 pts. 24-months probability of survival calculated from Kaplan-Meier method was 82.4%. In follow-up 80.9% of patients were in CCS class I and II. In SPECT, four months after CABG significantly more segments of left ventricle with normal perfusion (45% vs 53%; p < 0.05) were observed. Patients with LVEF < 40% are at higher operative risk because of often postoperative low output syndrome. Low output syndrome can by successfully treated with IABP. CABG significantly improves circulatory sufficiency in patients with LVEF < 40%.