Coronary artery by-pass grafting with internal mammary artery (IMA) has become the graft conduit of choice, due to improved survival and its long term patency rate. However, some studies have shown that, in comparison with saphenous vein grafts, after IMA grafting, there is increased postoperative impairment of pulmonary function, possibly due to the frequent performance of pleurotomy. In 57 consecutive patients, admitted for elective CABG with IMA, we prospectively evaluated the early (2nd and 6th day) postoperative chest X-ray complications and the late (2 months) respiratory function tests changes. Thirty-two patients had been subjected to pleurotomy (group 1) and 25 not (group 2). The incidence of pulmonary atelectasis and pleural effusion in 2nd and in 6th postoperative days was not different in the two groups: 22 vs. 19%, 74 vs. 52% in 2nd, and 29 vs. 19%, 48 vs. 38% in 6th postoperative day respectively. The incidence of elevated hemidiaphragm in 6th postoperative day was not different in the two groups (18.5 vs. 14%). Two months after surgery the mean values of spirometric tests were significantly lower than the preoperative values: VC from 88.5 +/- 1.26 to 80 +/- 1.65% of predicted, P < 0.001, FEV1 from 96.1 +/- 1.27 to 84.7 +/- 1.73% of predicted, P < 0.001, MEF50 from 84.9 +/- 3.14 to 69.2 +/- 3.18% of predicted, P < 0.001. No significant changes were detected in RV and in AaPO2.(ABSTRACT TRUNCATED AT 250 WORDS)