## **Core Concept**
Koch's triangle, also known as the triangle of Koch, is an anatomical region in the right atrium of the heart. It is defined by the intersection of the septal leaflet of the tricuspid valve, the coronary sinus orifice, and the tendon of Todaro. This triangle is clinically significant because it contains the atrioventricular (AV) node.

## **Why the Correct Answer is Right**
The AV node, located within Koch's triangle, receives its blood supply primarily from the **AV nodal artery**, which is usually a branch of the **right coronary artery (RCA)**. The RCA supplies a significant portion of the right atrium, the right ventricle, and often the AV node. This arterial supply is crucial for the functioning of the AV node, which acts as a critical delay in the electrical conduction pathway between the atria and ventricles.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although the left coronary artery does supply a significant portion of the heart, including parts of the atria and the AV node's blood supply can have variations, the primary and most consistent supply to Koch's triangle and the AV node comes from the right coronary artery.
- **Option B:** This option is incorrect because it does not accurately represent the primary blood supply to Koch's triangle.
- **Option D:** This option is incorrect because it likely represents another incorrect or less directly related coronary artery branch or a non-specific option.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the blood supply to the AV node is crucial for its function, and variations in coronary artery anatomy can affect this. Knowing that the AV node is typically supplied by a branch of the **right coronary artery** helps in understanding potential areas of ischemia and infarction that could affect AV node function.

## **Correct Answer:** C. Right coronary artery.