Arrhythmogenesis as an effect of antiarrhythmic therapy is a relatively recent concern. Satisfactory definitions are lacking, but 2 categories, clinical and technical, can be recognized. Although arrhythmogenesis is an international problem and multifactorial, its expression depends on variables that differ according to geographic location. In Europe, use of antiarrhythmic therapy is more conservative than it is in the U.S. In the U.S., many antiarrhythmic drugs commonly used in Europe are either recently released, are on limited release or are available only in investigational protocols. Mexiletine, class IC agents and sotalol are agents in routine use in Europe. All have arrhythmogenic potential, although this appears lowest with mexiletine.