Background: Incentive spirometry is used in addition to care, especially in reducing pulmonary complications after surgery. Complications in the cardiovascular and pulmonary systems can basically be determined by blood values and vital signs, which are important objective data of haemodynamics. Aim: This study aimed to test the hypothesis that the use of incentive spirometry in conjunction with postoperative pulmonary rehabilitation care has a notable impact on arterial blood gas, oxygen saturation (SpO2) and vital signs. Methods: This randomised, controlled trial used repeated-measures design. It was conducted between 2021 and 2022, and data from 58 patients who underwent coronary artery bypass graft surgery at the cardiovascular surgery clinic of a university hospital were analysed. All patients received pulmonary rehabilitation, and incentive spirometry was added for the experimental group. Results: In the experimental group, on post-op day 3, the arterial partial pressure of oxygen (PaO2) (p = 0.01), arterial oxygen saturation (SaO2) (p = 0.002) and oxygen saturation (SpO2) (p < 0.001) values were statistically significantly higher. Additionally, on post-op day 3 the experimental group had significantly lower systolic blood pressure (p = 0.03), diastolic blood pressure (p = 0.004) and respiratory rate (p < 0.001). Conclusion: Incentive spirometry after coronary artery bypass graft surgery improves oxygen levels and vital signs.