Summary

I doubt that you are really interested in a scientific definition of heartburn. Internet is filled with scientific information which gives you nothing useful. Though if you really interested in it click here.

Basic idea is that valve connecting oesophagus and stomach just doesn't work as expected and there is nothing modern medicine can do about this.

Drugs

Antacids. Great for short term symptom relief but longterm it will make it worse. Why? Because all it does is suppresses acid which is in your stomach at the moment you take it. But what happens next? That's an interesting part. Stomach still has some food in it and it gets signal that there is not enough acid in it. So it sends command to acid producing cells to produce more acid and fill stomach with it. So in one or two hours your heartburn usually gets back.

H2 receptor antagonists. I never personally tried them since my physicians recommended to go with PPI instead. Why? Because PPI is safer and stronger.

PPI. The best what is available on market now. Most recent drug approved by FDA is Nexium or so called purple pill. It is based on esomeprazole magnesium which is the latest drug approved by FDA for GERD treatment. For myself I mostly use Protonix (pantoprazole sodium) which is pretty much the same thing as Nexium but cheaper. There are also other PPIs like Aciphex (rabeprazole based) available on market.