Sunao Tawara's epoch-making work on the excitation conduction system of the mammalian heart paved the way for the advancement of modern cardiology in the 20th century. Even today, more than 90 years after the publication of the German monograph "Das Reizleitungssystem des Saugetierherzen", his precise account of the conduction system from the atrioventricular node through the His-Purkinje system to the ordinary ventricular muscle fibers retains all of its original actuality.This English edition of Tawara's monograph will serve as an invaluable reference for both basic and clinical cardiological research in the years ahead.