As the heart pumps, arteries, shown here in red, carry oxygen-rich blood away from the heart toward the body's tissues and vital organs. These include the brain, liver, kidneys, stomach, and muscles -- even the heart muscle.
At the same time, veins, shown here in blue, carry oxygen-poor blood from the tissues back to the heart. From there, it passes to the lungs to get more oxygen to take back to the heart so the cycle can repeat.
Review Date 7/12/2018
Updated by: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.