A double-blind, placebo-controlled, crossover, multicenter study was conducted to study the efficacy and safety of a single intravenous dose of sotalol (1.5 mg/kg over 10 minutes) in achieving normal sinus rhythm in paroxysmal supraventricular tachycardia (SVT) lasting greater than or equal to 15 minutes. Patients were randomized to either sotalol or placebo as initial treatment, and if the SVT was not terminated a crossover was performed after 20 minutes. A total of 43 patients were enrolled, 38 of whom with spontaneous (n = 14) or induced (n = 24) SVT were analyzed for sotalol efficacy. Most patients (n = 27) had atrioventricular (AV) nodal reentrant tachycardia, and an important subgroup (n = 11) had circus movement tachycardia, using an accessory pathway for retrograde conduction. The number of patients converting to sinus rhythm as a result of the initial treatment was significantly higher in the sotalol group than in the placebo group, for spontaneous (p less than 0.005) as well as for induced tachycardia (p less than 0.001). Sinus rhythm was achieved within 30 minutes in 83% of all patients who received sotalol as the first drug, compared with 16% of the patients first receiving placebo (p less than 0.0001). For sotalol safety analysis, 42 patients were included. A total of 37 patients received sotalol, 19 as the first treatment, and 18 as the second treatment, while 25 patients received placebo. A total of 15 possible adverse effects were reported, occurring in 10 patients with sotalol versus 4 with placebo. The only severe side effect (hypotension) necessitating termination of drug administration occurred with placebo. No proarrhythmic effects were observed.(ABSTRACT TRUNCATED AT 250 WORDS)