I was zip lining and at the end of the zip line was a block of about 50 pounds. I was going at about 30 mph and slammed my heel in it. Now it's purple and swollen. What should I do?

That's significant. B sure u get it evaluated by an orthopedic surgeon. May have a significant injury, don't miss ur chance 4 proper care, especially if there is a fracture.
See your doctor. You should see your doctor and see if they think you need an x-ray.
Heel injury. There is a chance you may've fractured your heel. Go to your doc or urgent care to have it examined and xray'd if needed.
Injury. Okay. This sounds like a normal reaction to an injury. Time will heal.