The part of the cardiac conduction system that excites contraction of the interventricular septum is the ________________.

The part of the cardiac conduction system that excites contraction of the interventricular septum is the Bundle of His.

Here's a step-by-step explanation:

1. The cardiac conduction system is a system of specialized heart muscle cells that conducts electrical impulses from the heart's sinoatrial node (also known as the "natural pacemaker") to the rest of the heart muscle.

2. The sinoatrial node sends an electrical impulse that spreads through the walls of the atria, causing them to contract.

3. This impulse then reaches the atrioventricular node, which is located at the bottom of the right atrium.

4. From the atrioventricular node, the impulse travels along the Bundle of His. This bundle is a pathway of fibers that runs down the middle of the heart, in the interventricular septum.

5. The Bundle of His splits into two branches, the right and left bundle branches, which carry the impulse to the bottom of the ventricles.

6. From there, the impulse spreads through the ventricles, causing them to contract. This contraction starts at the interventricular septum and spreads to the outer walls of the heart.

So, the Bundle of His is the part of the cardiac conduction system that carries the impulse that excites contraction of the interventricular septum.