To determine the safety and efficacy of intravenous adenosine as used in the emergency department (ED) for the treatment of presumed supraventricular tachycardia, the investigators performed a retrospective chart review in an urban, university-affiliated ED. Seventy-two consecutive patients were treated with intravenous adenosine for presumed supraventricular tachycardia. Of the 72 patients who were treated with adenosine, 46 patients had a confirmed diagnosis of supraventricular tachycardia. Of these, 39 of 46 (84.8%) converted to sinus rhythm after treatment. Of patients who successfully converted to sinus rhythm, none had recurrent tachycardia or required additional pharmacotherapy. Arrhythmias not successfully treated among the initially misdiagnosed patients were atrial fibrillation (n = 11), atrial flutter (n = 7), tachycardia of other origin (n = 5), and ventricular tachycardia (n = 2). No clinically significant adverse effects were noted among the study population. Intravenous adenosine is a safe and efficacious treatment for the emergent treatment of supraventricular tachycardia, including unstable patients (with hypotension and/or chest pain). It is also safe among patients initially presumed to have supraventricular tachycardia, who are later diagnosed with other arrhythmias.