**Question:** Reverse splitting of 2nd heart sound heard in -

A. Pulmonary hypertension
B. Cor Pulmonale
C. Congenital heart disease
D. Hypertrophic cardiomyopathy

**Core Concept:** The splitting of the 2nd heart sound (S2) is a result of the interaction between the pulmonary and mitral valves during the cardiac cycle. In a healthy heart, S2 is a single, non-splitting sound due to simultaneous closure of both valves. However, certain medical conditions can alter this normal pattern.

**Why the Correct Answer is Right:** In the context of the question, reverse splitting of S2 indicates the presence of a condition where the pulmonary valve opens before the mitral valve closes. This is seen in conditions with increased pulmonary vascular resistance, leading to a delay in pulmonary valve closure. One such condition is **B. Cor Pulmonale**.

**Why Each Wrong Option is Incorrect:**

A. **Pulmonary hypertension** is a condition with increased pulmonary vascular resistance, but the pulmonary valve opens after the mitral valve closes. This results in a split S2 with a long duration of the pulmonary component.

C. **Congenital heart disease** can lead to S2 splitting, but the cause of reverse splitting is diverse, encompassing various defects which do not specifically result in the delayed closure of the mitral valve.

D. **Hypertrophic cardiomyopathy** is characterized by increased wall thickness (hypertrophy) of the heart muscle, causing mitral valve dysfunction. This would result in a split S2 due to mitral valve regurgitation, not reverse splitting.

**Clinical Pearl:** Understanding the timing of valve closure and opening is crucial in interpreting heart sounds. Reverse splitting of S2 can be a useful clue for diagnosing conditions like Cor Pulmonale, which is a significant finding in the clinical examination.