Final answer:
The first heart sound, or S₁, is associated with the closing of the atrioventricular valves during ventricular contraction. The second heart sound, or S₂, is associated with the closing of the semilunar valves during ventricular diastole.
Step-by-step explanation:
In a normal, healthy heart, the first heart sound, known as S₁ or the 'lub' sound, is associated with the closing of the atrioventricular valves during ventricular contraction. The atrioventricular valves, including the mitral and tricuspid valves, separate the atria from the ventricles and prevent backflow of blood during contraction. When the ventricles contract, the pressure causes the atrioventricular valves to close, creating the 'lub' sound.
The second heart sound, known as S₂ or the 'dub' sound, is associated with the closing of the semilunar valves during ventricular diastole. The semilunar valves, including the aortic and pulmonary valves, separate the ventricles from the arteries and prevent backflow of blood into the ventricles. When the ventricles relax and blood flows out of the heart, the semilunar valves close, producing the 'dub' sound.