**Core Concept**
The AV node, or atrioventricular node, is a critical structure in the heart's electrical conduction system, responsible for delaying the electrical signal from the atria to the ventricles, allowing for proper coordinated contraction of the heart.

**Why the Correct Answer is Right**
The AV node is situated in the right atrium, specifically in the triangle of Koch, near the septal leaflet of the tricuspid valve. This location allows for the delay of the electrical signal, enabling the ventricles to fill with blood before contraction. The AV node contains specialized cells that can prolong the delay in the electrical signal, ensuring coordinated contraction of the heart.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the AV node is not located in the left atrium. The left atrium has its own distinct electrical conduction system.
**Option B:** Incorrect because the AV node is not situated in the right ventricle. The right ventricle receives the electrical signal from the AV node, but it is not the location of the AV node itself.
**Option C:** Incorrect because the AV node is not located in the pulmonary valve. The pulmonary valve is responsible for regulating blood flow from the right ventricle to the lungs.

**Clinical Pearl / High-Yield Fact**
The triangle of Koch, which contains the AV node, is a critical landmark for electrophysiologists performing procedures such as catheter ablation to treat arrhythmias.

**Correct Answer: C. Interventricular septum.**