The heart

The heart is the muscle that pumps blood rich in oxygen and nutrients to the body's tissues through the blood vessels.

The heart keeps blood moving in the body in a unidirectional way, it is a closed circuit, nothing is lost. The atria receive blood returning to the heart, the ventricles pump blood out of the heart.

Arteries carry oxygenated blood from the heart to the body's tissues. Nutrients are extracted from the tissues and returned through the veins. Veins carry blood back to the heart.

The heart's electrical system controls the speed of the heartbeat.