## Core Concept
The right heart border on a chest X-ray (CXR) is primarily formed by the structures of the right heart and adjacent mediastinal contours. The right heart silhouette is composed of several key structures that contribute to its border.

## Why the Correct Answer is Right
The right heart border on a CXR is mainly formed by the **superior vena cava (SVC)**, **right atrium (RA)**, and **inferior vena cava (IVC)**. The SVC and IVC are part of the venous return to the heart, and the right atrium forms the major part of the right heart border. The **azygos vein** also contributes to the right mediastinal border but is not considered a primary component of the right heart border itself.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not provided, but typically, structures like the SVC, RA, and IVC are correct components.
- **Option B:** Similarly, this option is missing but would likely represent a correct component if listed (e.g., SVC, RA).
- **Option C:** Without the specific details, we assume this could represent a correct structure (e.g., RA).
- **Option D:** This is the correct answer, **Right ventricle**. The right ventricle (RV) does not contribute to the right heart border on a CXR; instead, it forms part of the anterior cardiac silhouette, which is often not visible or only slightly visible on a standard CXR.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **right ventricle** does not contribute to the right heart border on a chest X-ray. The structures that do are the SVC superiorly, the right atrium in the middle, and the IVC inferiorly. This knowledge helps in localizing lesions or abnormalities seen on a CXR.

## Correct Answer: D. Right ventricle.