The human heart

The human heart is divided into four chambers, each of which serves its own function in the cycle of pumping blood. The atria are the thin walled upper chambers that gather blood as it flows from the veins between heartbeats. The ventricles are the thick-walled lower chambers that receive blood from the atria and push it into the arteries with each contraction of the heart.

The left atrium and ventricle work separately from those on the right. The role of the chambers on the right side of the heart is to receive oxygen depleted blood from the body tissues and send it on to the lungs; the chambers on the left side of the heart then receive the oxygen-enriched blood from the lungs and send it back out to the body tissues.