Final answer:
During the pause phase when the heart is resting, the ventricles are filling and the valves are closing to prevent blood from flowing back into the atria.
Step-by-step explanation:
During the "pause" phase, also known as diastole, the heart is resting and relaxing. During this phase:
- The ventricles are filling as blood flows from the atria into the ventricles.
- The valves are closing to prevent blood from flowing back into the atria.
Therefore, the correct answer is A) Ventricles are filling.