When you see spider veins and varicose veins on your legs and ankles, you might think only of what is visible to the eye. Chronic venous insufficiency is what's behind those problem veins. This condition occurs when, due to weakening or other factors, the valves that prevent blood from backing up in a part of a vein don't fully close. With each pump, then, some of the blood making its way back to the heart moves backward. This is referred to as reflux. Where there is blood pooling, the vein swells, resulting in visible discoloration, protrusion, and other symptoms. Chronic venous insufficiency isn't just a couple of visible veins here and there, it also causes other symptoms, including leg cramps or a sense of heaviness, discoloration or ulcers on the skin, aching, and more.