Dexmedetomidine for Reversal of Cocaine's Effects on the Heart

Inclusion Criteria: * Healthy adult subjects ages of 18-65 years without any history of substance abuse (other than tobacco), including narcotics, abuse of prescription painkillers, cocaine or any other recreational drug Exclusion Criteria: * Known or suspected right-to-left, bi-directional, or transient right-to-left cardiac shunts or detected by screening echocardiogram performed prior to I.V. infusion of Definity microbubbles * Hypersensitivity or prior reactions to Definity microbubbles * Pregnant or nursing women * Any evidence of cardiopulmonary disease by history or physical examination, including subjects who are taking any cardiovascular medications of any sort * History of hypertension or BP at time of consent \> 140/90 mm Hg * Any history of substance abuse (other than tobacco), including narcotics, prescription painkillers, cocaine or any other recreational drug (any person that says they have EVER tried these drugs will be excluded from this study) * Subjects reporting alcohol intake of more than 2 drinks/day * Severe psychiatric illness (e.g., schizophrenia, suicidal depression) in addition to drug dependence, which may signify a high risk of addiction * Diabetes mellitus or any other systemic illness * Individuals with a history of pseudocholinesterase deficiency * Hypersensitivity to dexmedetomidine or lorazepam * The presence of alcohol by breathalyzer * Subjects who have poor echocardiography images will be screen failed. * Persons with mechanically, magnetically, or electrically activated implants, such as cardiac pacemakers, neurostimulators, and infusion pumps (MRI only). * Persons with ferromagnetic implants and ferromagnetic foreign bodies, such as intracranial, aneurysm clips, shrapnel and intraocular metal chips as these could become dislodged (MRI only). * Persons unable to tolerate MRI imaging secondary to an inability to lie supine or severe claustrophobia (MRI only). * Persons whose renal function test does not meet CSMC standard of care MRI contrast protocol requirements (GFR \<45ml/min). * Persons with allergy to animal dander or animal-instigated asthma * Persons with a history of kidney or liver disease.