Fifty-two patients were randomized to receive either incentive spirometry (IS) or intermittent positive pressure breathing (IPPB) in addition to conventional chest physical therapy following coronary artery bypass grafting. Slow vital capacity and peak expiratory flow readings decreased rapidly and to an equal extent in both groups after surgery, and partly recovered by the sixth postoperative day (POP). Arterial PO2 values were similar for the groups on the first three POPs. On the POPs 2, 3, and 6, the number of chest films showing atelectases as well as the number of individual patients having atelectases revealed no statistically significant differences between the two groups. Based on the three variables studied, we consider both devices equal in efficiency after coronary surgery.