Physicians once found it convenient to think of cardiac arrhythmias as a sort of “itch” of the heart and of antiarrhythmic drugs as a soothing balm that, applied in sufficient quantities, would relieve the itch. During the past several decades, however, pioneering work has revealed many of the complexities of cardiac arrhythmias and of the drugs used to treat them. To the dismay of most reasonable people, the old, convenient viewpoint finally proved utterly false.