Objectives: To determine the effect preoperative use of an Incentive Spirometer (IS) has on preventing postoperative pulmonary complications among patients undergoing open heart surgeries. Methods: A prospective, randomized, controlled single-blinded parallel-group design. Data were collected from January 9th 2022 to April 1st  2022.  A total of n = 64 eligible patients were equally randomized to either intervention or control group. Patients in the intervention group performed preoperative IS training for two days before the scheduled surgery. The primary endpoint was the incidence of in-hospital PPCs. The secondary endpoints were postoperative Peak Expiratory Flow Rate (PEFR), Intensive Care Unit (ICU) stay, Hospital Length of Stay (HLOS). Results: Patients in the intervention group had a lower incidence of postoperative pulmonary complications compared to the control group (12.5% and 21.8%). There was a statistical significant difference between the two groups regarding postoperative PEFR, HLOS and intensive care unit stay. Conclusions: Preoperative rehabilitation (involving incentive spirometer is related to a lower incidence of postoperative pulmonary complications for the group that received the intervention. Training with preoperative incentive spirometer resulted in a shortening of hospital length of stay and Intensive Care Unit (ICU) stay. Trial registration: The study was registered in the Iranian Clinical Trial Registry, this at https://www.irct.ir/ reference number (IRCT20211224053503N1).