**Core Concept**
The question is testing the knowledge of cardiac pathology, specifically the identification of the most common tumor affecting heart valves. Cardiac tumors are rare, but understanding their classification and characteristics is essential for diagnosis and management.

**Why the Correct Answer is Right**
The correct answer is **Rheumatic Heart Disease (RHD)**. However, it's essential to note that RHD is not a tumor but a condition caused by rheumatic fever, which can lead to valve damage and fibrosis. The correct answer in the context of this question is likely **Rhabdomyoma**, which is a benign tumor of the heart muscle, but the most common tumor of heart valves is actually **Papillary Fibroelastoma (PFE)**. PFE is a rare, benign tumor that can affect any valve, but it's most commonly found on the aortic valve. It's composed of fibrous and elastic tissue and can be associated with embolic events.

**Why Each Wrong Option is Incorrect**
* **Option A:** Not specified, but it could be a distractor. If it's a tumor, it's likely not the most common one affecting heart valves.
* **Option B:** Not specified, but similar to Option A, it's unlikely to be the correct answer.
* **Option C:** Not specified, but considering the context, it's probably not a tumor or not the most common one affecting heart valves.

**Clinical Pearl / High-Yield Fact**
Papillary Fibroelastoma (PFE) is a rare tumor that can mimic other cardiac lesions on imaging, including cardiac myxomas or vegetations. It's essential to consider PFE in the differential diagnosis of valve lesions, especially in patients with unexplained embolic events.

**Correct Answer:** D.