For more than a century the heart sounds have played an important part in medical diagnosis. Their value to the clinician was stressed particularly by Laënnec, who devised the fundamental features of modern auscultation early in the nineteenth century. The association of the second sound with the closure of the semilunar valves is generally accepted. According to the familiar explanation given in a widely used textbook,1 the usual view is that the sound is due ultimately to the vibrations set up in these valves by their sudden closure; these vibrations are transmitted to the column of blood in the aorta (or pulmonary artery) and then to the intervening tissue of the chest wall.
The so-called first sound of the heart has not yielded so readily to a satisfactory explanation. It is admittedly related in some way to the function of the auriculoventricular valves. The chief difficulty in defining the
THE FIRST HEART SOUND. JAMA. 1933;101(1):36. doi:10.1001/jama.1933.02740260038014