During the beginning of ventricular diastole, as the ventricular pressure declines, a distinct acoustic event is detected through a stethoscope. Which of the following correctly identifies this event and its primary anatomical cause?

Step-by-step solution

During the beginning of ventricular diastole, the ventricles relax and the ventricular pressure falls below the pressure in the aorta and pulmonary artery. This pressure difference causes the blood to attempt to flow back into the ventricles, which forces the semilunar valves to close. The closure of the semilunar valves produces the second heart sound, known as 'dub'. The first heart sound ('lub') is produced at the beginning of ventricular systole due to the closure of the atrioventricular (bicuspid and tricuspid