Vagal maneuvers terminate new onset, catheter-induced paroxysmal supraventricular tachycardia (PSVT) in up to 92% of patients. The risk and benefit of vagal maneuvers for treating PSVT in the emergency department (ED) is inadequately defined. The purpose of this study was to determine the efficacy of nonpharmacological vagal interventions in converting spontaneous episodes of PSVT in adult patients and to derive a treatment plan for such patients based on clinical decision analysis. Seventeen adult patients who presented to the ED because of PSVT were treated with carotid sinus massage, Valsalva maneuver, and head-down tilt (alone and in combination). Only three patients converted out of PSVT with vagal intervention. The remainder received verapamil, which converted 12 of the 14 patients (86%) who received the drug (one required digoxin, one required synchronized cardioversion). Vagal maneuvers are safe in young, otherwise healthy patients but problems have been documented in the literature in older patients, who have a higher likelihood of coronary and/or cerebrovascular disease. Clinical decision analysis indicates that young patients should be treated initially with vagal maneuvers but that older patients (above approximately 65 years of age) should be treated initially with verapamil.