Coronary artery bypass grafting (CABG) is commonly performed with a saphenous vein graft (SVG) and/or an internal mammary artery graft (IMA). We hypothesized that there would be a higher incidence of pleural changes after CABG in patients who underwent IMA grafting because pleurotomy is usually performed. In the present study, the pre and the 6th postoperative day chest roentgenograms of 122 patients who received CABG were reviewed. The incidence of effusion in the patients who received only SVG was 43 percent (23/54) and did not differ significantly (p greater than 0.05) from the incidence in the patients who also had IMA 41 percent (28/68). Almost all of the patients (43/51) had unilateral left-sided pleural effusions. Most of the effusions were small and did not require treatment. The incidence of effusion was not higher in patients with enlargement of their cardiac silhouette or atelectasis and was not related to the presence of chest tubes. The incidence of pleural thickening was higher in the IMA group (49 percent) than in the SVG group (31 percent) but the difference did not achieve statistical significance (p greater than 0.05). We conclude that there is a high (approximately 40 percent) incidence of small effusions and thickening after CABG. The incidence of pleural effusion and pleural thickening do not appear to be influenced by the type of surgery (IMA vs SVG). We speculate that the effusions are due to pericardial inflammation.