Blood is carried away from the heart by arteries and back to the heart by veins. The heart pumps the blood downward to the feet but it is the contraction of the leg muscles that pumps the blood back upward to the heart.The primary leg muscle doing the pumping is the calf muscle. Each time the calf muscle contracts, blood is propelled upward thru veins past one-way valves. The valves prevent the backflow of blood in between muscular contractions. Varicose veins result when the one-way valves in the leg veins fail, which allows the blood to pool in the legs.