Venous leg ulcers are open sores that develop on the lower legs due to poor circulation. They are caused by a backup of blood in the veins of the legs, which can be caused by a variety of conditions, including deep vein thrombosis, varicose veins, and congestive heart failure. Venous leg ulcers can be painful and can take a long time to heal. Treatment typically involves compression therapy, wound care, and medications to reduce inflammation and improve circulation.