ObjectiveTo systematically evaluate the effects of tight glucose control (TGC) on clinical outcomes in post-cardiac surgery patients through an overview of systematic reviews. MethodsWe conducted comprehensive searches in Web of Science, Cochrane Library, JBI, PubMed, Embase, CINAHL, CBM, CNKI, WanFang Data, and VIP databases from inception to June 11, 2025. Two researchers performed literature screening, data extraction, quality assessment of included studies, and evidence quality evaluation independently. The corrected covered area (CCA) was calculated to assess the overlap of primary studies across included SRs/MAs. Meta-analysis was performed by using RevMan 5.3 software. ResultsA total of 11 SRs/MAs were included. The CCA was 10.43%. The results demonstrated that TGC reduced postoperative infection rates (RR=0.46, 95%CI 0.36 to 0.58, P<0.001) early mortality (RR=0.67, 95%CI 0.51 to 0.87, 0.003), and postoperative atrial fibrillation (POAF) incidence (RR=0.69, 95%CI 0.59 to 0.80, P<0.001), while shortening hospital stays (MD=?1.65, 95%CI ?2.38 to ?0.92, P<0.001), ICU duration (MD=?3.18, 95%CI ?4.80 to ?1.56, P<0.001), and mechanical ventilation time (MD=?2.95, 95%CI ?4.36 to ?1.54, P<0.001). However, it also increased the risk of postoperative hypoglycemia (RR=2.22, 95%CI 1.18 to 4.21, 0.01). Subgroup analyses demonstrated that TGC significantly reduced the risk of POAF in patients undergoing coronary artery bypass grafting (CABG) (RR=0.60, 95%CI 0.48 to 0.75, P<0.001). Conversely, in valve replacement patients, TGC was associated with a significant shortening of both intensive care unit stay (MD=?5.37, 95%CI ?10.50 to ?0.23, P=0.04) and duration of mechanical ventilation (MD=?2.04, 95%CI ?3.39 to ?0.68, 0.003). Moreover, the increased risk of postoperative hypoglycemia was predominantly seen in CABG patients (RR=3.95, 95%CI 2.22 to 7.05, P<0.001) and those with diabetes mellitus (DM) (RR=3.42, 95%CI 1.45 to 8.07, 0.005). ConclusionWhile TGC improved postoperative outcomes in cardiac surgery patients, its effects were heterogeneous across surgical types and patient cohorts, and it elevated the risk of hypoglycemia, particularly among CABG and DM patients. Due to constraints in evidence quality, further robust, large-scale studies are needed to confirm these findings.