Whether triggered activity plays a role in the genesis of cardiac arrhythmias is considered in this review. The characteristics of triggered activity are compared with those of automaticity and re-entry at the cellular electrophysiologic level, and these observations then are related to cardiac arrhythmias. We stress, however, that the relation between triggered activity and clinical arrhythmias still is largely speculative and that further experimental and clinical study is needed before the presence (or absence) of a role for triggered activity is verified.