**Core Concept**
The primary neoplasms of the heart are rare and can be benign or malignant. In adults, the most common type of primary heart tumor is a benign cardiac tumor, which can originate from various cardiac tissues.

**Why the Correct Answer is Right**
The correct answer is a cardiac myxoma, which is a type of benign cardiac tumor. Cardiac myxomas are known to arise from the endocardium, specifically from the mucous-producing cells of the atria. They often present with symptoms such as obstructive jaundice, palpitations, or systemic embolization due to tumor fragments breaking off and traveling to other parts of the body. The exact mechanism of myxoma formation is not well understood, but it is thought to be related to genetic mutations and abnormal cell proliferation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Rhabdomyoma is a type of benign cardiac tumor, but it is more commonly associated with tuberous sclerosis complex and typically occurs in children.
* **Option B:** Angiosarcoma is a type of malignant cardiac tumor, but it is much rarer than cardiac myxoma and often presents with more aggressive symptoms.
* **Option C:** Fibroma is a type of benign cardiac tumor, but it is more commonly associated with infants and children.

**Clinical Pearl / High-Yield Fact**
Cardiac myxomas are the most common primary heart tumor in adults, and they often present with obstructive symptoms due to their large size.

**Correct Answer:** D. Cardiac myxoma