Chronic venous insufficiency is a condition in which the veins in the legs have difficulty returning blood to the heart, causing blood to pool in the lower extremities. The condition occurs when one-way valves in the veins that normally help keep blood moving upward toward the heart, become weakened or damaged and can therefore no longer prevent the backflow of blood to the legs. As blood pools, various symptoms emerge, including pain, swelling, skin changes, and potentially ulcers.