Sunao Tawara: a father of modern cardiology

Knowledge of the conduction system of the heart was greatly advanced by Tawara's work carried out in Aschoff's laboratory in Marburg at the beginning of this century. In his monograph, The Conduction System of the Mammalian Heart, published in 1906, Tawara indicated that the treelike structure of specific muscle fibers comprising the atrioventricular node, His bundle, bundle branches, and Purkinje fibers served as the pathway for atrioventricular conduction of excitation in the mammalian heart. From his own anatomic and histological findings of the conduction system, he assumed precisely that the conduction velocity of excitation in the system, except in the atrioventricular node, would be fast and that contraction as the result of excitation would take place at the various sites of the ventricles almost simultaneously. According to Tawara, a long pathway to each contracting unit and a fast conduction velocity of excitation would be a prerequisite for the effective contraction of the ventricles. Tawara's findings and assumptions provided Einthoven the theoretical basis for interpreting the electrocardiogram, resulting in rapid popularization of electrocardiography. This century has witnessed the rapid progress of cardiology, including cardiac pacing and its related sciences. This progress has its roots in the discovery of the conduction system and the development of electrocardiography that took place almost in the same period at the beginning of this century. Tawara's pioneering work on the conduction system still serves as an invaluable reference for basic and clinical research.