Veins are the blood vessels that take the blood from your feet and legs back to the heart, ready for another cycle around the body. This means the blood in your leg veins should flow upwards. When your veins don’t work properly, they let blood flow backwards down the leg. This can cause you to have heavy, achy, tired or swollen legs, which feel worse when standing still. You get relief when you elevate your legs, as the bloods flows up the leg, back to the heart, under the influence of gravity.