If you clench your fist and then let it relax, the action is similar to the beating action of your heart. The human heart is a muscle, and incidently it is about the size of a fist. The heart actually lies in approximately the center of your chest. It is between the lungs and behind the protective breastbone. Blood keeps circulating through the body supplying cells with oxygen and nutrients needed for life because of the heart's constant beating action.

The human heart has four chambers. The atria are the upper two chambers where blood enters and leaves the heart and the lower chambers where the pumping action occurs are the ventricles. Valves permit blood to flow from each atrium to the ventricle just below it, but a thick wall or septum divides the right and left sides of the heart.

Heart Statistics

Beats per minute	70-80
Beats per day	100,000
Blood pumped when at rest (1 beat)	70 milliliters
Blood pumped when at rest (1 minute)	5 liters
Blood pumped when at rest (1 hour)	300 liters
Blood pumped during vigorous exercise (1 beat)	350 milliliters
Blood pumped during when at rest (1 minute)	25 liters
Blood pumped during when at rest (1 hour)	1500 liters
Time for blood from heart to reach big toe	60 seconds