**Core Concept**
Ebstein anomaly is a congenital heart defect characterized by the abnormal formation of the tricuspid valve and the right ventricle. It involves the **downward displacement of the tricuspid valve** into the right ventricle, leading to a small and dysfunctional right ventricle. This condition is often associated with other cardiac anomalies.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of Ebstein anomaly, which includes the **apical displacement of the tricuspid valve**, resulting in a small and non-functional right ventricle. This leads to **right heart failure** and **cyanosis** due to the increased pressure in the right atrium, causing blood to flow from the right atrium to the left atrium through an **atrial septal defect** or a **patent foramen ovale**.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Ebstein anomaly is not primarily characterized by an issue with the left side of the heart.
**Option B:** This option is incorrect as it does not accurately describe the tricuspid valve anomaly.
**Option C:** This option is incorrect because, although arrhythmias can occur, they are not the defining feature of Ebstein anomaly.

**Clinical Pearl / High-Yield Fact**
A key point to remember about Ebstein anomaly is that it often presents with **severe cyanosis** and **heart failure** in newborns, and it can be associated with **Wolff-Parkinson-White syndrome**, which is a condition that affects the heart's electrical pathways.

**Correct Answer:** D. Characterized by congenital downward displacement of a portion of the tricuspid valve into the right ventricle.