Veins before and after heat exposure. Nurses know that heat can make veins pop out more. This is why nurses will sometimes use hot packs or warming blankets on patients with poor vein access. When the body is cold, veins will constrict (vasoconstriction) and move deeper into the tissue. When the body becomes warm, veins will expand (vasodilation) and move more superficially in the tissue. I wanted to show this footage so that you can see the dramatic difference a little heat can make in th