If you are not sure which to use first after an injury, the ice or heat, then just remember this little tip. Ice relieves the swelling. Heat, on the other hand, relaxes the muscles.
For instance, if you twisted your ankle, the first thing you should do is apply some cold like a bag of frozen vegetables wrapped in a cloth or an ice pack. Keep this cold on the sore spot for about twenty minutes every few hours to help bring down the swelling.
However, if you overdo the housework or gardening and find yourself sore the next day, then heat will work better to relax those muscles. A moist electric heating pad that draws water from the air is amazing for this type of problem.