Postoperative pulmonary complications (PPCs) after coronary artery bypass graft (CABG) surgery are a major source of morbidity and mortality, and increase length of hospital stay and resource utilization. The prehospitalization period before CABG surgery may be used to improve a patient's pulmonary condition. The efficacy of preoperative inspiratory muscle training (IMT) in reducing the incidence of PPCs in high-risk patients undergoing CABG surgery has not yet been determined. To evaluate the prophylactic efficacy of preoperative IMT on the incidence of PPCs in high-risk patients scheduled for elective CABG surgery. A single-blind, randomized clinical trial conducted at the University Medical Center Utrecht, Utrecht, the Netherlands, with enrollment between July 2002 and August 2005. Of 655 patients referred for elective CABG surgery, 299 (45.6%) met criteria for high risk of developing PPCs, of whom 279 were enrolled and followed up until discharge from hospital. Patients were randomly assigned to receive either preoperative IMT (n = 140) or usual care (n = 139). Both groups received the same postoperative physical therapy. Incidence of PPCs, especially pneumonia, and duration of postoperative hospitalization. Both groups were comparable at baseline. After CABG surgery, PPCs were present in 25 (18.0%) of 139 patients in the IMT group and 48 (35.0%) of 137 patients in the usual care group (odds ratio [OR], 0.52; 95% confidence interval [CI], 0.30-0.92). Pneumonia occurred in 9 (6.5%) of 139 patients in the IMT group and in 22 (16.1%) of 137 patients in the usual care group (OR, 0.40; 95% CI, 0.19-0.84). Median duration of postoperative hospitalization was 7 days (range, 5-41 days) in the IMT group vs 8 days (range, 6-70 days) in the usual care group by Mann-Whitney U statistic (z = -2.42; P = .02). Preoperative IMT reduced the incidence of PPCs and duration of postoperative hospitalization in patients at high risk of developing a pulmonary complication undergoing CABG surgery. isrctn.org Identifier: ISRCTN17691887.