The first heart sound, known medically as S1, is the "lub." It is typically lower in pitch and lasts slightly longer than the second sound.
Physiology of Heart Sounds and Murmurs Authors: Michael A. Chizner, MD Journal: Heart Disease: A Textbook of Cardiovascular Medicine (often updated; look for chapters in Braunwald’s Heart Disease) OR a dedicated review in Current Problems in Cardiology Example modern review: "Heart Sounds: From the Physiology to the Bedside" — Journal of Cardiovascular Medicine (various years, e.g., 2018, 2022) what causes the lub dub sound of the heart
$S_1$ occurs roughly simultaneously with the palpable apex beat (the thrust of the left ventricle against the chest wall). The sound is actually composed of two distinct components—mitral closure followed milliseconds later by tricuspid closure—though they are usually perceived as a single sound. The first heart sound, known medically as S1, is the "lub
The familiar "lub-dub" sound of the heartbeat is a fundamental biological marker used to assess cardiovascular health. While often assumed to be the sound of the heart muscle contracting, acoustic analysis reveals that these sounds are primarily mechanical phenomena resulting from the sudden deceleration of blood flow and the abrupt closure of the heart valves. This paper explores the hemodynamic and anatomical mechanisms behind the first heart sound ($S_1$) and the second heart sound ($S_2$), distinguishing between valvular, muscular, and vascular contributions to the cardiac soundscape. The sound is actually composed of two distinct
After the ventricles have finished pumping blood into the main arteries, the pressure in those arteries becomes higher than the pressure inside the relaxing ventricles. To prevent blood from falling back into the heart, a second set of valves snaps shut: