Background: Patients receiving cardiac surgeries present high risk of developing postoperative complications. Incentive spirometry (IS) is used for the prevention and treatment of postoperative pulmonary complications in patients undergoing cardiac surgeries. Aim: Evaluate the effect of incentive spirometry on oxygenation and postoperative pulmonary complications after open heart surgery. Setting: The study was carried out in Cardiothoracic Department and open heart Intensive Care Unit at Sohag University Hospital. Subjects: A purposive sample of 60 adult patients undergoing open heart surgery they were reviewed for potential enrollment in the study.(30 study group) received routine hospital care in addition to incentive spirometer every 2 hours while the (30 control group) received routine hospital care only. Tools: Two tools were utilized to collect data Tool I:-Patient assessment sheet. Tool II: physiological Assessment sheet. Methods: Patients in the intervention group received bihourly use incentive spirometer for 72 hours. Results: Patients in the study group had a significantly lower mean number of hypoxic events with shorter duration and shorter length of stay in the hospital and the ICU. Conclusion: use of the incentive spirometer reduces the risk of pulmonary complications and hospital length of stay after cardiac surgery. Recommendations:  Offer a training program to refresh critical care nurses' knowledge about new deep breathing techniques, and teaching the patient how to perform incentive spirometry before surgery.