Alpha2-adrenergic agonist, dexmedetomidine, is recently used for sedation, analgesia or adjuvant to general anesthesia. Postsynaptic activation of alpha2 adrenoceptors in the central nervous system (CNS) inhibits sympathetic activity and thus can decrease blood pressure and heart rate. The blockade of sympathetic activity decrease the neuroendocrine stress response and may decrease the incidence of hypokalemia. The hypokalemia can increase the incidence of arrythmia, especially in cardiac patients. We postulated that dexmedetomidine could decrease the neuroendocrine stress response, thus decrease arrhythmia during cardiac surgery. Furthermore, dexmedetomidine have been reported to have cardioprotective effect with previous animal studies.