The rhythm of the heart, its normal functioning and pathologic disturbances, has been a favored subject of investigation by clinical and basic scientists in recent decades. This heightened interest and attention was stimulated by the somber and surprising revelations from epidemiologists and pathologists of the enormity of the number of sudden arrhythmic deaths in the Western world, and the concurrent advancement of technology for recording and control of electrical activity of the heart. Technological advancements have included the recording of intracellular potentials from cardiac cells,...