This study investigates the effects of dexmedetomidine (Dex) pretreatment in patients undergoing cardiac valve replacement under cardiopulmonary bypass. In the Dex group, the time to the first rescue dose of propofol was longer, and the total propofol dosage was less than in the control group. Additionally, the Dex group showed reduced cardiac injury markers and inflammation, requiring less mechanical ventilation time than the control group. The findings suggest that Dex pretreatment offers myocardial protection and optimizes postoperative outcomes.