Thump-thump. Thump-thump. Did you know that the heart beats over 100,000 times each day? Your heart pumps blood through your body. Your heart beats more slowly when you sit still, and it beats faster when you exercise.

The heart is a special organ with four chambers, or hollow sections, inside. Between the chambers are one-way valves that keep the blood moving in the correct direction through the heart. The sound of these valves closing is the thump-thump you hear.