**Core Concept**
Cardiac polyp refers to a rare, benign cardiac tumor that originates from the endocardium, specifically from the papillary muscles or chordae tendineae. This tumor is composed of fibrous and muscular tissue, which can lead to obstruction of blood flow or even cardiac arrhythmias.

**Why the Correct Answer is Right**
The cardiac polyp is a type of benign cardiac tumor that arises from the endocardium, which is the innermost layer of the heart. This type of tumor is characterized by the presence of fibrous and muscular tissue, which can lead to obstruction of blood flow or even cardiac arrhythmias. The exact pathogenesis of cardiac polyp is not well understood, but it is thought to be related to the abnormal proliferation of endocardial cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Cardiac polyp is not a type of cardiac tumor that arises from the myocardium.
**Option B:** Cardiac polyp is not a type of cardiac tumor that is associated with a poor prognosis.
**Option C:** Cardiac polyp is not a type of cardiac tumor that is typically found in children.

**Clinical Pearl / High-Yield Fact**
Cardiac polyps are often asymptomatic and may be discovered incidentally on echocardiography. However, if they become large enough, they can cause significant symptoms such as shortness of breath or palpitations.

**Correct Answer:** D.