BACKGROUND: The present study aimed to describe the long-term alterations of pulmonary function and also to describe its association with post-operative pain after coronary artery bypass grafting (CABG) surgery. METHODS: In this prospective study, thirty non-smoker male patients undergoing isolated on-pump CABG were consecutively included in this study. Pulmonary function measurements were performed, in a sitting position, preoperatively, a week postoperatively, and 6 months after the surgery using a Medical Graphics PF/Dx pulmonary function system. Pain was determined by using visual analog scale (VAS) pain scores with a standardized questionnaire’s. RESULTS: Regarding functional class, all patients had New York Heart Association (NYHA) Class II to III. A week after operation, a severe restrictive pulmonary impairment was revealed with a mean decrease in VC to 60.9 ± 9.2% and in forced expiratory volume in one second (FEV1) to 64.6 ± 12.2% of pre-operative values (P < 0.001). Regarding sternotomy related pain, the mean pain VAS score was preoperatively 3.3 ± 1.5 that reached to 6.2 ± 2.5 and 4.8 ± 2.2 1 week and 6 months after the operation (P < 0.001). The trend of the changes in pain score within 6 months of operation was significantly similar to the trend of the changes in some pulmonary function indices such as FEV% and residual volume (RV). CONCLUSION: A significant reduction is expected in most pulmonary functional parameters following CABG despite normal pulmonary function state preoperatively. Severe pain originated from sternotomy may be an important factor related to pulmonary dysfunction following CABG.