As the heart pumps, the arteries carry oxygen-rich blood (shown in red) away from the heart and toward the body's tissues and vital organs. These include the brain, liver, kidneys, stomach, and muscles, including the heart muscle itself. At the same time, the veins carry oxygen-poor blood (shown in blue) from the tissues back toward the heart. From there, it passes to the lungs to receive more oxygen. This cycle repeats itself when oxygen-rich blood returns to the heart from the lungs, which pumps it throughout the body.
Update Date 9/15/2014
Updated by: Robert Hurd, MD, Professor of Endocrinology and Health Care Ethics, Xavier University, Cincinnati, OH. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.