Johannes Purkinje (1787–1869) was a prolific Czech anatomist and physiologist. 1 He established the first Department of Physiology in the world in 1839 in Prussia. He was the first to use a microtome to obtain thin tissue sections for microscopic examination and was the first to describe sweat glands. He introduced the terms “plasma” and “protoplasm.” He made major contributions to the study of vision, including discovery of the Purkinje effect, the Purkinje shift, and Purkinje images. He discovered two types of Purkinje cells: large neurons in the cerebellum and, of particular interest to cardiac electrophysiologists, large cardiac muscle fibers specialized for rapid conduction along the endocardium of the ventricles. 1

Purkinje fibers differ in numerous ways from working myocardial cells. The relative sizes of Purkinje and myocardial cells are species-dependent. 2–5 In general, Purkinje cells are larger than myocardial cells and are distinguishable histologically. 2 Purkinje cells lack transverse tubules that are present in myocardial cells. 6 Because of their primary role in rapid conduction of the electrical impulse, Purkinje cells have fewer myofibrils than myocardial cells. As a result, microscopically they appear lighter than myocardial cells. The amount of glycogen in Purkinje fiber is much higher than that in myocardial cells. 7 The glycogen can be metabolized anaerobically which may make Purkinje cells more resistance to hypoxia than working myocardial cells, 7 although some evidence suggests that the opposite is true. 8