Anesthesia is a drug induced, reversible, comatose state that facilitates surgery and it is widely assumed that cognition returns to baseline after anesthetics have been eliminated. However, many patients have persistent memory impairment for weeks to months after surgery. Cardiac surgery appears to carry the highest risk of postoperative cognitive dysfunction (POCD). These cognitive deficits are associated with increased mortality, prolonged hospital stay and loss of independence. The investigators propose to investigate the role of Dexmedetomidine (DEX) in preventing long-term POCD after cardiac surgery and enhancing early postoperative recovery. It is anticipated that DEX will be the first effective preventative therapy for POCD, improve patient outcomes, and reduce length of stay and healthcare costs.