In the early days of open heart surgery, acute respiratory failure following extracorporeal circulation was a significant deterrent to an uncomplicated recovery. Although a marked improvement in prevention and treatment of postoperative respiratory failure has been achieved, the problem has not been completely eliminated and continues to be a causative factor in morbidity and mortality Fates following open heart surgery. We have attempted to evaluate postoperative respiratory failure in patients undergoing cardiac operation with the aid of extracorporeal circulation. Our series comprised 92 patients who underwent elective open heart surgery at the Department of Thoracic and Cariodvascular Surgery, School of Medicine, Kyungpook National University, from January, 1980 to December, 1982. In our study, the overall incidence of acute respiratory failure following open heart surgery was 18.8 percent. The duration of extracorporeal circulation in a series of 18 patients who developed postoperative respiratory failure [Group B] was longer in the mean value [120.3 minutes] than the uncomplicated 74 patients [Group A] [85.8 minutes]. The duration of artificial ventilation after open heart surgery in Group A averaged 13.4 hours as contrasted with 76.5 hours in Group B. In Group B, the inspired oxygen concentration [FiO2] in artificial ventilation was continued in the higher level than Group A until 18 hours after operation. Upon pulmonary function test performed pre-and postoperatively, residual volume[RV], RV/TLC and FEV 1.0/FVC were remained essentially unchanged following extracorporeal circulation, whereas forced vital capacity [FVC], FEV 1.0 and FEF 25-75% were significantly decreased in the early postoperative days. The incidence of acute respiratory failure was significantly higher in a series of patients who developed postoperative complications, such as re- exploration due to massive bleeding, low cardiac output, acute renal failure and arrhythmias. A total of 9 patients died, giving an overall mortality was 33.3 percent whereas the mortality was only 1.1 percent for patients without respiratory failure.