Chronic venous insufficiency (CVI) is a medical condition in which blood pools in the veins, straining the walls of the vein. The most common cause of CVI is superficial venous reflux which is a treatable condition. As functional venous valves are required to provide for efficient blood return from the lower extremities, this condition typically affects the legs. If the impaired vein function causes significant symptoms, such as swelling and ulcer formation, it is referred to as chronic venous disease. It is sometimes called chronic peripheral venous insufficiency and should not be confused with post-thrombotic syndrome in which the deep veins have been damaged by previous deep vein thrombosis. Most cases of CVI can be improved with treatments to the superficial venous system or stenting the deep system. Varicose veins for example can now be treated by local anesthetic endovenous surgery.