**Core Concept**
The Valsalva maneuver increases pressure in the thoracic cavity, which affects the hemodynamics and cardiac output. In certain cardiac conditions, this increased pressure can lead to changes in the intensity or characteristics of murmurs, allowing for a more accurate diagnosis.

**Why the Correct Answer is Right**
In Hypertrophic Obstructive Cardiomyopathy (HOCM), the murmur of obstruction increases with the Valsalva maneuver due to the increased pressure in the left ventricle. This is because the Valsalva maneuver increases the pressure in the thoracic cavity, which in turn increases the pressure in the left ventricle, thereby increasing the obstruction of blood flow through the left ventricular outflow tract (LVOT). This results in a louder murmur due to the increased pressure gradient across the LVOT.

**Why Each Wrong Option is Incorrect**
**Option A:** Mitral stenosis typically produces a low-pitched, rumbling murmur that increases with inspiration (with increased venous return) and decreases with expiration, not the Valsalva maneuver.

**Option C:** Ventricular Septal Defect (VSD) typically produces a pansystolic murmur that may increase with exercise or increased flow, but not specifically with the Valsalva maneuver.

**Option D:** Aortic stenosis typically produces a harsh, crescendo-decrescendo systolic murmur that may increase with exercise or increased flow, but not specifically with the Valsalva maneuver.

**Clinical Pearl / High-Yield Fact**
The Valsalva maneuver can be used to differentiate between HOCM and other cardiac conditions by observing the change in the intensity of the murmur. If the murmur increases with the Valsalva maneuver, it is more likely to be HOCM.

**✓ Correct Answer: B. HOCM**