AIMS: The use of metformin during the perioperative period remains a contentious issue. This study aimed to assess the impact of metformin use on overall mortality rates among patients in postoperative cardiac intensive care units. MATERIALS AND METHODS: This study retrospectively analyzed data from 8675 cardiac surgery patients sourced from the Medical Information Marketplace in Intensive Care (MIMIC 3.0) database. The administration of metformin during the postoperative ICU stay was assessed. Utilizing Cox proportional hazards modeling, the study explored the correlation between metformin treatment and all-cause mortality (ACM). The impact of metformin on survival rates was examined using the Kaplan-Meier method. Subgroup analyses and interaction tests were conducted to ascertain the consistency of these associations across diverse demographic and clinical subgroups. RESULTS: The average age of participants in this study was 69.0 years, spanning from 61.0 to 76.0 years. A higher proportion of individuals who received metformin following surgery were male (75.6% vs 72.3%, P = 0.01), younger (67.19 ± 9.26 vs 67.95 ± 11.75, P = 0.006), and had lower Sequential Organ Failure Assessment Scores (4.92 ± 2.38 vs 5.31 ± 2.79, P < 0.001). When compared with patients who did not receive metformin after surgery, these individuals who received metformin following surgery had a lower prevalence of chronic kidney disease, congestive heart failure, and peripheral vascular disease and the higher prevalence of acute myocardial infarction, hypertension and diabetes. The metformin administration was correlated to decreased ACM at 28, 60, 90, and 365 days. CONCLUSIONS: Utilizing metformin in the intensive care unit following surgery was correlated with the notable reduction in ACM among patients who have undergone cardiac procedures, particularly those with diabetes. However, further prospective research is necessary to validate these findings.