Background: The aim of the study was to examine the relationship between preoperative pulmonary function and outcomes after cardiac surgery. Methods: We performed preoperative pulmonary function tests (PFTs) in 1,169 patients undergoing cardiac surgery at the Minneapolis Veterans Affairs Medical Center. Airway obstruction was defined as forced expiratory volume in 1 minute (FEV1) to forced vital capacity ratio <0.7. Results: Of the 1,169 patients, 483 (41%) had a prior history of chronic obstructive pulmonary disease (COPD). However, 178 patients with a history of COPD had no airway obstruction on PFT. Conversely, 186 patients without a COPD history had airway obstruction on PFT. Thus, PFT results helped reclassify the COPD status of 364 patients (31%). Operative mortality was 2% in patients with no or mild airway obstruction versus 6.7% in those with moderate or severe obstruction (ie, FEV1 to forced vital capacity ratio <0.7 and FEV1 <80% predicted). Postoperative mortality was higher (odds ratio 3.2, 95% CI 1.6-6.2, P = .001) in patients with moderate or severe airway obstruction and in patients with diffusing capacity of the lung for carbon monoxide <50% of predicted (odds ratio 4.9, 95% CI 2.3-10.8, P = .0001). Notably, mortality risk was 10× higher (95% CI 3.4-27.2, P = .0001) in patients with moderate or severe airway obstruction and diffusing capacity of the lung for carbon monoxide <50% of predicted. Conclusions: These data show that PFT before cardiac surgery reclassifies the COPD status of a substantial number of patients and provides important prognostic information that the current risk estimate models do not capture.