The objective of this study is to evaluate the efficacy of the modified shock index (MSI) in predicting the incidence of postoperative cardiovascular events (PCEs) in patients with pre-existing cardiac disease undergoing non-cardiac surgery. A retrospective analysis was performed on the clinical data of patients who underwent gastric, colorectal, and hepatobiliary surgeries at Union Hospital Affiliated to Fujian Medical University between January 2020 and December 2025. Baseline characteristics, intraoperative vital signs, occurrence of postoperative cardiac complications, and total postoperative hospital stay were reviewed and summarized to assess the predictive performance of the MSI for PCEs in this patient population.