The relationship between the duration of postoperative mechanical ventilation and pre-, intra- and just post-operative factors was studied in 48 patients undergoing coronary artery bypass grafting with cardiopulmonary bypass. The patients were divided into 2 groups on the basis of the duration of mechanical ventilation: group A with less than 24 hours (n=35) and group B with more than 24 hours (n=13). Investigation of the perioperative parameters which significantly correlated with the duration of mechanical ventilation revealed that emergency case, cardiac dysfunction, high dose administration of cathecolamine, high left atrial pressure (LAP), low serum albmin, and renal dysfunction after transfer to intensive care unit (ICU) were found to be increased risks of postoperative respiratory failure.