A common misconception is that the heart sounds are produced by the contracting myocardium (heart muscle). While the muscle contraction drives the pressure changes required for valve movement, the muscle tissue itself is relatively silent. If the valves were removed, the contracting heart would produce very little sound. Therefore, the "lub-dub" is best categorized as a valvular and hemodynamic event rather than a muscular one.
Unlike $S_1$, the components of $S_2$ are often distinguishable. The aortic valve ($A_2$) typically closes slightly before the pulmonary valve ($P_2$) due to lower resistance in the systemic circuit compared to the pulmonary circuit. This results in a phenomenon known as "physiological splitting," which can sometimes be heard during inhalation. what causes the lub dub sound of the heart
The first heart sound, or $S_1$, corresponds to the beginning of ventricular systole (contraction). It is characteristically longer and lower in pitch than the second sound. A common misconception is that the heart sounds
As the ventricles squeeze, the pressure inside them rises sharply. To prevent blood from flowing backward into the upper chambers (the atria), two specific valves snap shut: Located on the left side of the heart. Therefore, the "lub-dub" is best categorized as a
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The human heart functions as a dual-pump system, responsible for the continuous circulation of blood through the pulmonary and systemic circuits. This cyclic activity produces a rhythmic acoustic signature known to medical professionals as the cardiac cycle sounds. Colloquially termed "lub-dub," these sounds are the acoustic result of the heart's mechanical pumping action. Understanding the etiology of these sounds is essential for diagnosing various cardiac pathologies. This paper aims to demystify the causes of the heart sounds by examining the physiological events of systole and diastole.
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)