The often emergent nature of life-threatening cardiac dysrhythmias, the frequent seeming "resistance" of the abnormal heart rhythm to therapy, and the commonly encountered toxicity of antidysrhythmic agents combine to make treatment of cardiac dysrhythmias one of the strictest challenges to the practicing physician. Although electrophysiologic studies have markedly increased out understanding of dysrhythmogenesis and the actions of anti-dysrhythmic drugs, these numerous investigations have provided but little assistance to the practicing physician either as an intellectual framework or as a guide to patient care. The electrophysiologic classification of the antidysrhythmic drugs presented in this paper should be acceptable both to the electrophysiologist and the clinician since it is based on alterations in basic membrane properties and correlates well with clinical realities. It serves as a guide to initial drug selection, anticipated bioelectric complications, the use of alternative drugs, and combination antidysrhythmic therapy.