At what structure is ventricular excitation considered complete?

Ventricular excitation is considered complete at the Purkinje fibers, which are specialized conducting fibers that spread throughout the ventricles. The Purkinje fibers facilitate rapid conduction of electrical impulses that have traveled through the conduction system of the heart, including the bundle of His and the left and right bundle branches.

Once the impulse reaches the Purkinje fibers, it allows for a synchronous contraction of the ventricular myocardium, ensuring that the ventricles contract effectively and simultaneously. This process is crucial for efficient pumping of blood from the heart to the lungs and the rest of the body.

Other structures mentioned, such as the SA node and AV node, are key components of the heart's conduction system, but they primarily function in the initiation and propagation of impulses rather than the completion of ventricular excitation. The aortic valve is involved in regulating blood flow out of the ventricles but does not participate directly in the electrical conduction process. Thus, the completion of ventricular excitation is marked by the activity of the Purkinje fibers.