Arterial disease and vein disease are part of the same branch of medicine, known as vascular disease, which is defined as any condition that affects and impairs the circulatory system. Your arteries and your veins have different purposes within this system. Arteries carry oxygen- and nutrient-rich blood from the heart and lungs to other parts of the body, and veins carry the deoxygenated blood and waste materials back to the heart and lungs for renewal and recirculation. Diseases of both the arteries and the veins are serious, but some forms of vascular disease are more dangerous than others.