**Core Concept:** A pansystolic murmur is a continuous murmur heard throughout the cardiac cycle. A soft first heart sound indicates a reduced intensity of the initial sound of heartbeat. These two findings combined suggest an issue with the left ventricle.

**Why the Correct Answer is Right:** The correct answer is option C, **Hypertrophic Cardiomyopathy (HCM)**. In HCM, there is an abnormal and excessive growth (hypertrophy) of the cardiac muscle fibers in the left ventricle, leading to a thickened heart wall and reduced left ventricular compliance. This results in a reduced ejection fraction and increased afterload, causing the pansystolic murmur at the apex and the soft first heart sound.

**Why Each Wrong Option is Incorrect:**
A. **Aortic Stenosis (AS):** In AS, the narrowing of the aortic valve restricts blood flow from the left ventricle to the aorta. A pansystolic murmur is heard at the apex due to increased turbulence, but the first heart sound remains normal or may be slightly elevated due to the increased afterload.

B. **Aortic Regurgitation (AR):** In AR, there is leakage of blood from the aortic valve into the aorta, causing increased blood volume flow. This results in a pansystolic murmur at the apex, but the first heart sound remains normal due to the normal or elevated second heart sound.

C. **Hypertrophic Cardiomyopathy (HCM):** As explained above, HCM results in a thickened left ventricle, reduced compliance, and reduced ejection fraction. This leads to a pansystolic murmur at the apex during diastole and a soft first heart sound due to reduced left ventricular compliance.

D. **Coarctation of Aorta:** This condition involves a narrowing of the aorta, causing increased blood pressure in the upper body and decreased blood pressure in the lower body. A pansystolic murmur is heard at the apex due to increased turbulence, but the first heart sound remains normal.

**Clinical Pearl:** HCM is a common cause of pansystolic murmur at the apex and a soft first heart sound. It is important for students to recognize this combination of findings to narrow down the differential diagnosis and prompt further evaluation for potential cardiovascular disease.