No. Nexium is the trade name of a generic drug called esomeprazole, a proton pump inhibitor used to treat gastro-esophageal acid reflux. “Nitrates for chest pain” refers to the class of cardiac drugs that share a similar biochemical structure structure and pharmacologic mechanism, which involves conversion to nitric oxide. In the U.S., the available nitrates are:
- isosorbide mononitrate
- isosorbide dinitrate
These are vasodilators, used for anginal chest pain, usually in combination with beta blockers. They work by dilating the arteries around the heart and improving blood flow.
A google search reveals that C4 is a dietary supplement that contains caffeine. I suspect that the warning about nitrates has to do more with identifying people who have cardiac problems (which could be exacerbated by caffeine) than any specific drug interaction.
I have no idea why your chest was on fire, and this site is not a good place to try to find out. You should certainly discuss this with your doctor if you’re concerned.