**Core Concept**
Aortic stenosis is a narrowing of the aortic valve opening, which can lead to obstruction of blood flow from the left ventricle to the aorta. This can result in symptoms such as dyspnea, chest pain, and syncope due to the inability of the heart to pump enough blood to meet the body's needs.

**Why the Correct Answer is Right**
The mechanism behind aortic stenosis is the thickening and calcification of the aortic valve leaflets, which reduces the valve's ability to open fully. This can lead to a significant increase in left ventricular pressure, causing symptoms such as dyspnea, chest pain, and syncope. The decreased cardiac output can also lead to fatigue, weakness, and even syncope.

**Why Each Wrong Option is Incorrect**
* **Option A:** While heart failure can present with similar symptoms, it is not the most likely diagnosis in this case due to the specific combination of dyspnea, chest pain, and syncope.
* **Option B:** Pulmonary embolism typically presents with sudden onset of dyspnea, tachypnea, and tachycardia, but is less likely to cause syncope.
* **Option C:** Myocardial infarction can present with chest pain and dyspnea, but is less likely to cause syncope in the absence of other symptoms.
* **Option D:** Hypertrophic cardiomyopathy can present with syncope, but is less likely to cause chest pain and dyspnea in the absence of other symptoms.

**Clinical Pearl / High-Yield Fact**
The combination of dyspnea, chest pain, and syncope in a 61-year-old patient should raise suspicion for aortic stenosis, and prompt further evaluation with echocardiography and cardiac catheterization.

**Correct Answer:** C. Aortic stenosis.