**Core Concept**
The Valsalva maneuver involves forced exhalation against a closed glottis, increasing intrathoracic pressure and affecting cardiac filling and cardiac output. Certain murmurs are influenced by this hemodynamic change, allowing for their identification.

**Why the Correct Answer is Right**
During the Valsalva maneuver, the increased intrathoracic pressure reduces venous return to the heart, leading to a decrease in left ventricular volume. This decrease in ventricular volume reduces the pressure gradient across the aortic valve, leading to a decrease in the intensity of aortic regurgitation murmurs. In contrast, murmurs associated with increased flow across the aortic valve, such as those caused by aortic stenosis or hypertrophic cardiomyopathy, may increase in intensity during the Valsalva maneuver due to the increased resistance to flow.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because mitral regurgitation murmurs typically decrease in intensity during the Valsalva maneuver due to decreased left ventricular volume and reduced regurgitant flow.
**Option B:** Incorrect because tricuspid regurgitation murmurs are not directly affected by the Valsalva maneuver, as the right ventricle is not directly influenced by the increased intrathoracic pressure.
**Option C:** Incorrect because pulmonary regurgitation murmurs may actually decrease in intensity during the Valsalva maneuver due to decreased right ventricular volume and reduced regurgitant flow.

**Clinical Pearl / High-Yield Fact**
The Valsalva maneuver can be used to differentiate between aortic stenosis and aortic regurgitation murmurs. Aortic stenosis murmurs typically increase in intensity during the Valsalva maneuver, while aortic regurgitation murmurs typically decrease.

**Correct Answer:** A. Aortic stenosis murmurs increase in intensity during the Valsalva maneuver.