Your veins carry blood back toward the heart. Tiny vessels called capillaries in organs and tissues of the body deliver deoxygenated blood into small veins called venules, which join to form veins. Blood flows through the veins to the body's two main veins (called the vena cavae), which deliver the blood back into the heart.
Source: AMA's Current Procedural Terminology, Revised 1998 Edition. CPT is a trademark of the American Medical Association.