Objective: To investigate the prevalence and impact of abnormal respiratory patterns in cardiac surgery patients. Design: Prospective cohort study. Setting: Tertiary hospital. Participants: Patients scheduled for elective coronary artery bypass graft surgery. Interventions: None. Measurements and Main Results: Pulmonary function tests were performed in 454 patients before surgery. Abnormal respiratory patterns were defined as follows: obstructive (forced expiratory volume in 1 s [FEV1]/forced vital capacity [FVC]