Which heart sound occurs in early diastole due to rapid opening of a stenotic mitral valve?

The opening snap is a characteristic heart sound that occurs during early diastole, specifically associated with the rapid opening of a stenotic mitral valve. In the setting of mitral stenosis, the valve's thickened leaflets do not open smoothly, leading to a distinct sound as they open. This sound is heard shortly after S2, typically indicative of the sudden reduction in left atrial pressure as blood rapidly flows from the left atrium into the left ventricle.

In contrast, the third heart sound is usually a normal finding in young individuals and occurs due to rapid ventricular filling, while the fourth heart sound is an abnormal finding associated with atrial contraction and is common in conditions that result in a stiff or hypertrophied left ventricle. Splitting of S2 relates to the timing difference between the closure of the aortic and pulmonary valves during the respiratory cycle and is not specifically tied to mitral valve abnormalities. Therefore, the correct association with early diastole and a stenotic mitral valve is the opening snap.