In this Emergency Department (ED)-based study, the investigators evaluated a standardized modified Valsalva maneuver (MVM) as first-line therapy and compared intravenous (IV) adenosine with IV diltiazem among patients with persistent atrioventricular nodal re-entrant tachycardia (AVNRT)-consistent supraventricular tachycardia (SVT) after MVM, focusing on successful conversion to sinus rhythm. The investigators also assessed drug-related adverse events and clinically relevant treatment-course measures.