Despite the almost complete disappearance of the so called "postperfusion lung syndrome" after cardiac surgery with extracorporeal circulation (ECC), there is still a need for respiratory treatment in some cases, primarily for cardio-circulatory or respiratory reasons. In addition postoperative artificial ventilation is provided routinely in many centers for at least a few hours, until stabilization of cardio-circulatory and metabolic state is achieved. In 4 groups (I-IV) with a total of 659 patients (18 to 72 years old) undergoing open cardiac surgery for acquired heart disease (I: aortic valve, II: mitral valve, III: multivalvular disease, IV: coronary artery disease) postoperative cardio-circulatory and pulmonary complication rate, duration of artificial ventilation needed, PaO2 and some influencing factors have been evaluated. Group II and III show the highest rate of complications, 15.5 and 19.8% respectively, versus 7.7 and 8.1% in group I and IV respectively. The mean duration of postoperative respiratory treatment in cases with complications within all groups (133--156 h) is about 6 times the duration of respiratory treatment in the non complicated cases (23--24 h). In all 4 groups mean PaO2 at the time of extubation is lower for the complicated compared with the non complicated cases. Age of patients, severity of disease, preoperative pulmonary function, prolonged duration of ECC and myocardial ischemia have been found to be predisposing factors for postoperative cardio-pulmonary complications, whereas the duration of anesthesia and the type of anesthesia do not show any influence.