Which one among the following statements regarding heart sound is correct?

Heart sounds are primarily generated by the mechanical actions of the heart valves during the cardiac cycle. The first heart sound (S1), often described as 'lub', is produced by the closure of the atrioventricular (mitral and tricuspid) valves at the onset of ventricular contraction [t2][t6][t10]. The second heart sound (S2), or 'dub', occurs when the semilunar (aortic and pulmonary) valves snap shut following ventricular ejection [t2][t5][t8]. While blood flow turbulence contributes to the audible vibrations, the definitive cause of the distinct sounds heard during auscultation is the opening and closing of these valves [t1][t3][t4]. Conversely, 'murmurs' are not normal heart sounds; they are abnormal, whooshing noises caused by turbulent blood flow, often indicating underlying valve pathology such as stenosis or regurgitation [t4][t7][t9].

Sources

1. [1] https://en.wikipedia.org/wiki/Heart_sounds
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK541010/