**Core Concept**
Pulmonary artery wedge pressure (PAWP) and left ventricular end-diastolic pressure (LVEDP) are both measures of left atrial pressure. A gradient between these pressures can indicate an obstruction to left atrial emptying, typically caused by a mass or other structure in the left atrium.

**Why the Correct Answer is Right**
A left atrial myxoma is a type of benign tumor that can grow in the left atrium and obstruct blood flow. This obstruction leads to an increase in left atrial pressure, which is reflected as an increase in PAWP. However, the LVEDP remains normal because the obstruction is at the level of the left atrium, not the left ventricle. This results in a gradient between the two pressures.

**Why Each Wrong Option is Incorrect**
**Option A:** Aortic regurgitation would lead to an increase in LVEDP due to the backflow of blood from the aorta into the left ventricle, but it would not cause a gradient between PAWP and LVEDP.

**Option B:** Constrictive pericarditis would lead to an increase in both PAWP and LVEDP due to the restriction of ventricular filling, and there would not be a gradient between the two pressures.

**Option D:** Pulmonary thromboembolism would lead to an increase in PAWP due to the obstruction of blood flow in the pulmonary arteries, but it would not cause a gradient between PAWP and LVEDP.

**Clinical Pearl / High-Yield Fact**
A key feature of left atrial myxoma is the presence of a gradient between PAWP and LVEDP, which is a classic exam-trap to remember. This is because the obstruction to left atrial emptying is at the level of the left atrium, not the left ventricle.

**Correct Answer:**
✓ Correct Answer: C. Left atrial myxoma