Conventional pulmonary rehabilitation programs improve exercise tolerance, peripheral muscle strength, and health related quality of live but not pulmonary function in patients with chronic obstructive pulmonary disease (COPD). The role of breathing retraining techniques in the rehabilitation of patients with COPD remains unclear. The hypothesis to be tested in this study is that pulmonary function, cardio-pulmonary exercise capacity, health related quality of life and cardiac autonomic modulation of patients with COPD who undergo pulmonary rehabilitation plus breathing retraining will be better than that of patients undergoing a conventional pulmonary rehabilitation.