More commonly know as a heal spur, I had it several years ago, also ran a lot. Had 3 cortisone shots, Dr. said ideally I should notice the about 1/3 of the pain disappear with each shot. Worked pretty much according that plan. Note that this form of treatment treats the symptons, not the cause. Still it has been close to 10 years since my last shot and the pain has not returned. The heal plate in a different post also treats the symptons, only way to get rid of it is to have it removed.
Running pounds on everything. Not sure if this has a permanent negative effect but it sure inflames it in the short term. While I still go for the occassional 5 mile run (once a month or so) without aggravating the foot, I generally use the non impact cardio equipment at the gym these days. Let pain be your guide, might want to find an alternate way of getting your cardio if running aggravates the symptons.