@Scrbblechick -- Very true about 911, but if the person isn't allergic to aspirin, I'd also give two full strength with a little water. My doctor advised me to do that when I was having chest pains. Thank the Lord it was just a panic attack! But I'd never had one before, so I had no idea what was going on. I just knew I thought I was having a heart attack. Of course, with a panic attack, the fear feeds the panic, which magnifies every symptom.
Most people know if they're allergic to aspirin. I'd say give a BC or Goody's powder if there are any around, since those tend to work very quickly, assuming the person isn't allergic. But call 911 first, every time, before doing anything else. And take a Red Cross CPR class. You never know when you might need it.