Final answer:
The electrical events responsible for the action potential of the ventricles involve a wave of depolarization that begins in the right atrium and spreads to the contractile cells.
Step-by-step explanation:
The electrical events responsible for the action potential of the ventricles begin with the wave of depolarization in the right atrium. This impulse then spreads across the superior portions of both atria and down through the contractile cells. The contractile cells then start contraction from the superior to the inferior portions of the atria, effectively pumping blood into the ventricles.