With a heel warmer.
2 heel warmers - one on the heel and one on the calf.
I never liked heel warmers, you get increased blood flow if you run a diaper under warm water and not only wrap the foot, but up the leg as far as it will go. This gives you a good blood flow and you can quickly get your test done and sent to the lab so you can take care of your baby.
I wrap the warmer I wrap the warmer around the heel or have parent hold on fingers while I prepare all of mt supplies. Works like a charm.
I have found that if you warm both heels at the same time the infant tolerates the heel stick much better. Or, for PKUs or bilis where I need a good amount of blood, I will wrap a heel warmer around the foot and then wet a diaper with warm water and wrap that around the heel warmer. Hope this helps!