Of 142 adult patients undergoing open-heart surgery, 123 were extubated either in the operating room or within 3 hours after admission to the recovery room, to avoid the discomfort and risks of prolonged mechanical ventilation. The remaining 19 patients, who had impaired cardiac function, were mechanically ventilated for 1 to 7 days postoperatively. The most important criteria for cardiopulmonary malfunction indicating the need for continued mechnical ventilation were a low mixed venous O2 saturation (SVO2) of less than 60% and a high left atrial pressure (greater than 20 torr). Of the 123 patients, 118, had an uneventful postoperative recovery and 5 needed reintubation, 2 because of low SVO2 and 3 because of complications unrelated to respiratory management. Most adult patients can spontaneously breathe adequately immediately after or within 3 hours of completed open-heart surgery, but a thorough physiologic and clinical evaluation should precede extubation, to identify those who need prolonged mechanical ventilation in the postoperative phase. Criteria for selection of patients for early extubation are presented.