The Mechanism of the Generation of the Third and Fourth Heart Sounds

A simple unitarian concept of the mechanism of third and fourth sounds is presented. This study demonstrates that the third sound occurs during early rapid diastolic ventricular filling at a time when atrial pressure exceeds ventricular pressure. It is recorded within the ventricle and on the ventricular wall. It coincides with ventricular muscle vibrations. The fourth sound is demonstrated to consist of two components, both occurring when atrial pressure exceeds ventricular. The first component coincides with the peak of atrial contraction, is recorded within the atria, and is inaudible. The second component, which is audible (25 to 70 cycles per second) and follows the first by 0.01 to 0.02 second, is recordable within the ventricle coinciding with the impact of blood from atrial systole against the ventricular wall. These observations demonstrate that the audible third and fourth heart sounds have a common origin in the ventricles and have the same temporal and hemodynamic relationships regardless of etiology.