## **Core Concept**
The right border of the heart on a chest X-ray (CXR) is primarily formed by the superior and inferior vena cavae and the right atrium. Understanding the cardiac silhouette and its borders is crucial for interpreting CXRs, especially in diagnosing cardiac abnormalities.

## **Why the Correct Answer is Right**
The correct answer involves understanding the normal cardiac anatomy as seen on a CXR. The right border of the heart is formed by:
- The **Superior Vena Cava (SVC)**, which is the superior part.
- The **Right Atrium (RA)**, which constitutes the major part of the right heart border.

## **Why Each Wrong Option is Incorrect**
- **Option A: Pulmonary artery** - The pulmonary artery contributes to the left heart border, specifically the main pulmonary artery and its branches, not the right border.
- **Option D: Rt ventricle** - The right ventricle does not contribute to the right heart border on a CXR because it is anterior and does not outline the cardiac silhouette's border; it is mainly the right atrium that does.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is the "right heart border" on a CXR is primarily made up of the **Superior Vena Cava (SVC) superiorly** and the **Right Atrium (RA) inferiorly**. This knowledge helps in identifying abnormalities such as an enlarged right atrium.

## **Correct Answer:** B.