The Physiologic Basis of the Heart Sounds

¹ Professor and Director, Division of Cardiovascular Research; Professor of Medicine
² Associate Professor and Associate Director, Division of Cardiovascular Research; Associate Professor of Physiology

(1) The mechanism of production of the heart sounds is re-examined and new experimental and clinical evidence is reported.

(2) While the first and second heart sounds are not caused by valve closure per se, it is concluded that they are caused by vibrations set up both in the closed valves and in the cardiac and vascular structures surrounding them. These vibrations are proportional to the rapidity of tension, as revealed by the first derivative of either left ventricular pressure (first sound) or of the aortic-left ventricular pressure difference (second sound).

(3) The third sound, which in the past had been related to flow peak or valve reclosure, seems caused by an intrinsic property of the ventricular wall and is related to diastolic volume, due to either increased filling or greater residual volume.