Aim: One major cause of postoperative respiratory complications is pulmonary atelectasis. Atelectasis and the associated loss of functional alveolar units has been recognized as a major pathophysiological mechanism responsible for postoperative hypoxemia after coronary artery bypass graft (CABG). The aim of this study was to determine which therapeutic breathing method from incentive spirometry (IS), non-invasive intermittent positive pressure breathing (IPPB) and continuous positive airway pressure breathing (CPAP) in addition to postoperative pulmonary physiotherapy obtain the best improvement in blood gases in phase I of cardiac rehabilitation program after CABG. Method: Thirty six patients of both sexes who underwent CABG divided into three groups. Group (A) received breathing training with IS (5 minutes 5 times per day) in addition the chest physiotherapy program for patients after CABG and Group (B) received breathing training with CPAP (10 cmH2O for 15 minutes once daily) in addition to the chest physiotherapy program for patients after CABG., where Group(C) received breathing training with IPPB (maximum 15 cmH2O for 15 minutes once daily) in addition to the chest physiotherapy program for patients after CABG. Measurements of blood gases were done before the study in the first post operative day and repeated at the end of the study in the tenth postoperative day. Result: Blood gases were improved in all groups in addition to a significant difference between IS & CPAP and IS & IPPB groups. Where there was no significant difference between CPAP & IPPB groups. Conclusion: Incentive spirometry in addition to the usual respiratory physical therapy is recommended for patients in phase I of cardiac rehabilitation program after CABG.