Dexmedetomidine in Children Having Transthoracic Echocardiography

Inclusion Criteria: * Outpatients scheduled to receive sedation for transthoracic echocardiography * Subject must be a candidate for both types of anesthetic and both doses of dexmedetomidine * Must be 3 months to 36 months of age Exclusion Criteria: * The subject has a history of cardiac conduction system disease (e.g. 1st or 2nd degree AV block) or channelopathy (e.g. long QT). * The subject is taking digoxin, alpha-adrenergic or beta-adrenergic agonist or antagonist (e.g., clonidine, propranolol, albuterol), anti-arrhythmic medications, or vasodilators (e.g. ACE inhibitors) * The subject has received a dose of any other sedative within 48 hours. * The subject has life-threatening, medical conditions (American Society of Anesthesiologists Physical Status 4, 5). The American Society of Anesthesiologists (ASA) classification scale is a measure of physical status or how healthy the patient is. For our study, we will focus on children which are defined as ASA I, II or III which means a healthy child (ASA I), a child with a systemic disease that is mild and well controlled (ASA II) or a child with systemic disease that is severe and controlled (ASA III). * The subject is allergic to or has a contraindication to any of the drugs used in the study. * The subject has previously been treated under this protocol. * The subject has severe coarctation of the aorta (risk of exaggerated vasoconstriction) * The subject has Moyamoya disease (risk of recurrent stroke)