Your legs are made up of a network of veins. Healthy leg veins contain valves that open and close to assist the return of blood back to the heart. Venous reflux disease develops when the valves that keep blood flowing out of the legs and back to the heart become damaged or diseased. This can cause blood to pool in your legs and lead to symptoms such as pain, swelling, swollen limbs, leg heaviness and fatigue, skin changes and skin ulcers, and varicose veins.