Pulmonary complications after cardiac surgery are a leading cause of postoperative morbidity and mortality. Respiratory muscle weakness may contribute to the postoperative pulmonary abnormalities. We hypothesized that: (1) there is a decrease in inspiratory muscle strength (PImax at residual volume) and endurance (Pmpeak/PImax) following coronary artery bypass graft (CABG); (2) this weakness is associated with reduced pulmonary function tests (PFTs), impaired gas exchange, and a higher rate of pulmonary complications; and (3) prophylactic inspiratory muscle training (IMT) can prevent those changes. Eighty-four candidates for CABG, with ages ranging from 33 to 82 years, were evaluated prior to operation and randomized into two groups: 42 patients underwent IMT using a threshold trainer for 30 min/day for 2 weeks, 1 month before operation (group A); 42 patients served as a control group and underwent sham training (group B). There was a significant decrease in respiratory muscle function, PFTs, and gas exchange in the control group following CABG, whereas these parameters remained similar to those before entering the study in the training group. The differences between the groups were statistically significant. In addition 11 (26%) patients in the control group but only 2 (5%) in the training group needed postsurgical mechanical ventilation longer than 24 hours, CABGs have a significant deteriorating effect on inspiratory muscle function, PFTs, and arterial blood gases. The decrease in these parameters can be prevented by prophylactic inspiratory muscle training, which may also prevent postsurgical pulmonary complications.