Background: After coronary artery bypass surgery, pulmonary complications and oxygenation disorders are common, which have an important role in mortality and morbidity. Different methods are used for the improvement of pulmonary function and oxygenation, of which incentive spirometry (IS) has been investigated here. The aim of this study is to evaluate the effects of IS on arterial blood gases after coronary artery bypass graft (CABG). Materials and Methods: This was a clinical trial. Fifty patients who were candidates for CABG were chosen. The patients had been allocated to two random groups of intervention and control. The intervention was done through IS. These two groups were compared for the arterial blood gases' preoperative level, and the levels on first (after extubation), second, and third postoperative days. Results: The study findings showed that on the third postoperative day, there was a significant difference between the intervention and control groups in the mean amount of arterial blood oxygen (82.3 ± 4.7 vs. 72.7 ± 7.1, respectively, P = 0.02), arterial blood carbon dioxide (36.8 ± 2 vs. 43.7 ± 3.2, respectively, P = 0.007), and oxygen saturation (96.8 ± 1.4 vs. 90.5 ± 1.4, respectively, P = 0.03). Conclusions: This investigation shows that using IS is significantly effective in the improvement of blood arterial gas parameters.