THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -The first sound LUB is produced when the atrioventricular valves i.e. tricuspid and bicuspid valves close at the start of ventricular systole. The second sound DUB is produced at the beginning of ventricular diastole when the pulmonary and aortic semilunar valves close.

Detailed explanation-2: -S2. The second heart sound, called S2, makes a “dub” sound caused by the closure of the semilunar (aortic and pulmonary) valves following ventricular systole.

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.