Abstract Cardiovascular complications in patients undergoing thoracic surgery, which physicians have a limited ability to predict, are often unavoidable and resulting in adverse outcome. Cardiopulmonary exercise testing (CPET), the gold standard of cardiopulmonary function evaluation, has also been proved to be a preoperative risk assessment tool. Meanwhile, elevated red blood cell distribution width (RDW) has surged as a biochemical marker in the occurrence of cardiovascular disease. However, it is yet unclear the value of CPET combined with RDW in predicting cardiovascular complications after thoracic surgery. 50 patients with cardiovascular complications after thoracic surgery were collected as the case group, and 100 thoracic surgery patients were recruited as the control group, with the same gender, age ± 2 years old, and no postoperative complications. After admission, all patients underwent CPET and RDW inspection before surgery, and the results were recorded. The CPET parameter oxygen pulse (VO2/HR) and RDW of the case group were lower than those of the control group (P