Overview of the Venous System :
The venous system constists of veins that return blood from the body to the heart. In the leg, blood normally flows from the superficial veins, which are near the skin surface, to the perforator veins. The deep veins return blood to the heart.
There are valves within the venous system that ensure that blood flows in one direction to the heart and does not flow backwards. There is also a muscle in the calf of the lower leg, the "calf muscle pump," which helps to push the blood up the legs to the heart.