Background It is controversial whether pulmonary function testing should be performed routinely in cardiac surgery patients. The aim of our study was to focus on patients who have congestive heart failure, caused by left ventricular dysfunction or left-sided heart valve disease, and study the prognostic value of performing preoperative pulmonary function testing on their postoperative outcomes Methods: This is a retrospective propensity score matched study that included 366 patients with congestive heart failure who underwent cardiac surgery and had preoperative pulmonary function test. The patients were divided into two groups: Group 1; who had a normal or mild reduction in pulmonary function tests and group 2; who had moderate to severe reduction in pulmonary function tests. The postoperative outcomes, including pulmonary complications, were compared between the two groups. Results Pulmonary function tests were normal or mildly reduced in 190 patients (group 1) and moderately to severely reduced in 176 patients (group 2). Propensity matching identified 111 matched pairs in each group with balanced preoperative and operative characteristics. Compared to group 1, Group 2 had longer duration of mechanical ventilation [12 (7.5- 16) vs. 9 (6.5- 13) hours, p<0.001], higher postoperative Creatinine [111 (90- 142) vs. 105 (81- 128) µmol/dl, p=0.02] and higher hospital mortality (6.31% vs 0%, p=0.02). Conclusion In congestive heart failure patients undergoing cardiac surgery, moderate to severe reduction of pulmonary function test was associated with longer duration of mechanical ventilation and higher hospital mortality.