Objective: To investigate the cardioprotective effect of the continuous administration of dexmedetomidine using serum cardiac troponin I (cTnI) and creatine kinase MB (CK-MB) concentrations as biomarkers during off-pump coronary artery bypass grafting (OPCAB) surgery. Design: A prospective, randomized, parallel-group controlled study. Setting: A university hospital. Participants: One hundred sixteen patients undergoing OPCAB surgery. Interventions: Patients were divided randomly into 3 experimental groups that were separated by the dexmedetomidine administration protocol: a high-dose group (loading dose, 1 mu g/kg; maintenance dose, 0.6 mu g/kg/h); low-dose group (loading dose, 0.6 mu g/kg; maintenance dose, 0.3 mu g/kg/h); and control group (the same amount of 0.9% saline as placebo). Serum cTnI and CK-MB levels were measured before surgery and 24 hours and 48 hours after surgery. Measurements and Main Results: Serum cTnI and CK-MB levels in patients of the high-dose group were less than those of the other 2 groups 48 hours after surgery. The administration of dexmedetomidine significantly decreased the heart rate. Compared with the control group, there was a significantly reduced requirement of sevoflurane in the other 2 groups (p < 0.05). The intraoperative and postoperative cumulative volumes of urine output in the high-dose group were greater than those of the other 2 groups (p < 0.05). The authors also found that the extubation time and length of stay in the intensive care unit were prolonged in the high-dose group. Conclusions: Myocardial damage was reduced by the administration of a 1 mu g/kg loading dose and a 0.6 mu g/kg/h infusion dose of dexmedetomidine. However, further studies are needed to understand the underlying mechanism and to confirm that high doses of dexmedetomidine could be administered safely in patients undergoing OPCAB surgery. (C) 2016 Elsevier Inc. All rights reserved.