A total of 106 patients participated in a clinical investigation to determine the incidence and etiology of pulmonary complications following myocardial revascularization with the internal mammary artery graft; 39 patients (group I), undergoing valve replacement or myocardial revascularization with vein grafts, served as control. The mammary artery was used for revascularization in the remaining patients. The pleura was opened during the dissection of the mammary graft in 34 patients (group II), but was left intact during harvesting of the internal mammary artery in 33 patients (group III). Inspiration and expiration chest X-rays were obtained during the first 3 months of convalescence to determine the presence of pleural fluid, the position of the left hemidiaphragm, and to asses diaphragmatic movement. Pleural effusions, left lower-lobe atelectasis, and elevation of the left hemidiaphragm were observed in all groups after operation, but were more commonly observed in those patients undergoing revascularization with the mammary artery graft. Postoperative chest X-rays just prior to discharge from hospital were normal in 69% of the control group, only 9% of patients in group II who had pleurotomy during mammary artery dissection, and 42% of group III. By 3 months, however, 95% of patients in groups I and II had normal chest X-rays, whereas 53% of patients in group II had persistent loss of left-lung volume related to the presence of left-lower-lobe atelectasis, left pleural effusions and organization of the postoperative hemothorax.(ABSTRACT TRUNCATED AT 250 WORDS)