I've had this once or twice from running. My wife has had it off and on for years. A couple of things that help:
1) Get a foam roller or "the stick" and stretch the heck out of your calves and hamstrings. Do this many times a day.
2) Do eccentric calf exercises: http://www.sportsinjuryclinic.net/sport ... tendinitis
Make sure that when you are raising your heel, you're doing it with the other foot.