Ancillary Effects of Dexmedetomidine Sedation After Cardiac Surgery

Inclusion Criteria: 1. 18-85 years old; 2. Scheduled for cardiac surgery with bypass (CABG, valve, or combined); 3. Able to provide a written informed consent; 4. Hemodynamically stable (heart rate\>= 55). Exclusion Criteria: 1. Sick sinus syndrome or Wolff-Parkinson-White syndrome 2. Atrio-ventricular block 3. Hypersensitivity or known allergy to dexmedetomidine 4. Hepatic disease, e.g. twice the normal level of liver enzymes 5. Atrial fibrillation within 1 preoperative month; 6. Permanent pacemaker; 7. Use of amiodarone or dexmedetomidine within the last 30 days; 8. Patients with an ejection fraction under 30% or who had severe heart failure 9. Myocardial infarction in the previ¬ous 7 days; 10. Body mass index =\< 40 (BMI= mass (kg) / height (m)2); 11. Those taking clonidine within last 48 hours.