ANATOMY

Detailed explanation-1: -The first heart sound (S1) represents closure of the atrioventricular (mitral and tricuspid) valves as the ventricular pressures exceed atrial pressures at the beginning of systole (point a). S1 is normally a single sound because mitral and tricuspid valve closure occurs almost simultaneously.

Detailed explanation-2: -The two major heart sounds are “lub” (from the closure of AV valves) and “dub: (from the closure of aortic and pulmonary valves).

Detailed explanation-3: -The first heart sound (S1) is composed of several high-frequency components; only the first two are normally audible. These two sets of audible vibrations are temporally related to closure of the mitral and tricuspid valves.

Detailed explanation-4: -The first heart sound (S1) is produced by vibrations generated by closure of the mitral (M1) and tricuspid valves (T1). It corresponds to the end of diastole and beginning of ventricular systole and precedes the upstroke of carotid pulsation.

Detailed explanation-5: -This tension on the AV valve leaflets prevents them from bulging back into the atria and becoming incompetent (i.e., “leaky”). Closure of the AV valves results in the first heart sound (S1). This sound is normally split ( 0.04 sec) because mitral valve closure precedes tricuspid closure.