Numerous antiarrhythmic agents with differing pharmacologic properties and side effects had been shown to suppress ventricular arrhythmias. It had also been postulated that antiarrhythmics might raise an individual's threshold for experiencing ventricular fibrillation. There had been several published reports of large (at least l00 patients), long-term clinical trials of antiarrhythmic agents in post-MI patients. None of these had yielded statistically significant results using mortality as the response variable. This might have been due to incorrect drug selection, inadequate sample size, inappropriate choice of patients, or the lack of impact of arrhythmia treatment on mortality.