Final answer:
D. An opening snap. The sound occurring in early diastole caused by a rapid opening of a stenotic mitral valve is an opening snap. It is associated with mitral stenosis.
Step-by-step explanation:
The sound occurring in early diastole caused by a rapid opening of a stenotic mitral valve is an opening snap. In a normal, healthy heart, there are only two audible heart sounds: S1 and S2. S1 is the sound created by the closing of the atrioventricular valves during ventricular contraction and is normally described as a 'lub,' or first heart sound. The opening snap occurs when the stenotic mitral valve opens rapidly during early diastole, creating a sharp sound. This sound is often associated with mitral stenosis, a condition where the mitral valve narrows, impeding blood flow from the left atrium to the left ventricle.