**Core Concept**
The Valsalva maneuver increases intrathoracic pressure, which in turn affects the volume of blood in the heart chambers. This results in a change in the pressure gradient across the cardiac valves, leading to changes in the intensity of certain murmurs.

**Why the Correct Answer is Right**
The murmur that increases with the Valsalva maneuver is typically a mid-systolic ejection murmur associated with left ventricular outflow tract obstruction, such as that seen in hypertrophic cardiomyopathy. During the Valsalva maneuver, the decreased venous return to the heart increases the left ventricular outflow tract obstruction, leading to an increase in the intensity of the murmur.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely referring to a diastolic murmur, which would not increase with the Valsalva maneuver. Diastolic murmurs are related to issues with diastolic filling of the heart, such as aortic regurgitation or mitral stenosis, and are not affected by changes in intrathoracic pressure.
* **Option B:** A systolic ejection murmur associated with pulmonary stenosis would not increase with the Valsalva maneuver. In fact, it might decrease due to the decreased right ventricular volume and pressure.
* **Option D:** An apical systolic murmur associated with mitral regurgitation would not increase with the Valsalva maneuver. The murmur intensity is more related to the volume of regurgitant blood and the presence of a significant ventricular volume overload.

**Clinical Pearl / High-Yield Fact**
The Valsalva maneuver is a useful clinical tool for differentiating between various cardiac murmurs. It is essential to understand how different murmurs behave with changes in intrathoracic pressure to accurately diagnose and manage cardiac conditions.

**Correct Answer: C.**