Which two valves closing produce the second heart sound (Dub)?

The second heart sound, commonly referred to as "Dub," is produced by the closure of the aortic and pulmonary valves at the beginning of diastole. When the heart contracts, blood is ejected from the ventricles into the aorta and pulmonary artery. Once the ventricles finish contracting and begin to relax, the pressure in the aorta and pulmonary artery exceeds that in the ventricles, causing the aortic valve and pulmonary valve to close. This closure generates the characteristic sound of "Dub."

In contrast, the mitral and tricuspid valves are responsible for the first heart sound, "Lub," which occurs with their closure when the ventricles contract. Understanding this mechanism is critical in physiology as it relates to the cardiac cycle and the sounds associated with heart function.