This study analyzed 8186 adult patients undergoing cardiac surgery to examine the impact of perioperative hemoglobin decrease (ΔHb) on red blood cell transfusion outcomes. Patients with greater hemoglobin decreases (≥50%) were found to have higher risks of complications like mortality and organ failure. Transfusions helped in some cases but became harmful when exceeding four units. The findings underscore the importance of careful transfusion management in cardiac surgery.