Final answer:
The rhythmic expansion of an artery as the heart beats is referred to as the pulse, which occurs due to the ventricles contracting during ventricular systole and pushing blood out of the heart.
Step-by-step explanation:
The term for the rhythmic expansion of an artery as the heart beats is pulse. After blood is ejected from the heart, the arteries expand to accommodate the blood and recoil. This pulse can be palpated manually or measured electronically. During the cardiac cycle, both the atria and ventricles undergo systole (contraction) and diastole (relaxation). Atrial diastole is when the atria relax, and following this, ventricular systole occurs when the ventricles contract, pushing blood out of the heart.