The ongoing flow of blood from the heart to the body and back to
the heart again is called circulation. Blood vessels carry blood
throughout your body. Veins are the vessels that return blood to
the heart. Anatomy of a Vein Veins have cuplike flaps called
valves spaced along their inside walls. Valves open upward, so
blood can move up the vein. Valves close to keep blood from
falling back down the vein.