During every generation since Rouanet advanced the theory that all heart sounds are purely valvular, a few outstanding cardiac specialists have supported that view.1Many physiologists and most writers of medical textbooks have accepted the compromise that the first sound and the gallop sounds are partly muscular in origin, and not a few men distinguish the muscular from the valvular element in describing their auscultatory observations. An attempt to distinguish the muscular and valvular elements in experiments on dogs ended in demonstrating that the first sound was purely valvular,2since vigorous contractions occurred with no audible vibration when venous filling was cut off or the auriculoventricular groove compressed with a ligature which closed off the arterial outlets as well. A study of our records of human heart sounds and those reported by Lewis,3Wolferth and Margolies4and Houssay5has strengthened the conviction that the three