The effect on the human third heart sound of variations in the rate of filling of the heart.

The first descriptions of the physiological third heart sound (Gibson, 1907; Hirschfelder, 1907) related its occurrence to the presence of a wave in the venous pulse immediately following the V wave. Thayer (1908) showed that the sound occurs simultaneously with the downstroke of the V wave or the upstroke of the wave that immediately follows; this corresponds to the period in the cardiac cycle when the rate of filling of the ventricles is maximal, just after the opening of the atrio-ventricular valves. Because of its time of occurrence the third heart sound has been called the " rapid-filling " sound. The physiological third heart sound is best heard at, or a short distance medial to, the cardiac apex, with the subject recumbent and lying on the left side. On auscultation it seems louder if the rate of venous return of blood to the heart is increased by moderate exercise (Gallavardin, 1912), by raising the patient's arms and legs (Thayer, 1909), or by pressure on the abdomen (Gibson, 1907). Observers who attempted to record the third heart sound by phonocardiography after exercise have differed in their findings. Bridgman (1915) found an increase in the sound deflections immediately after exercise, whereas Mannheimer (1940) found a diminution. The improved electronic techniques employed in modern phonocardiography offer an opportunity to demonstrate objectively any alterations in loudness of the heart sounds with varying rates of venous inflow of blood. Linear, stethoscopic, and logarithmic phonocardiograms may be recorded as recommended by Rappaport and Sprague (1942). The deflections on the linear records vary in size with the amplitude of the original vibrations. The deflections on the logarithmic records vary with the loudness of the original sounds as heard by the human ear.