Prilosec is a PPI (Proton Pump Inhibitor). It basically stops the stomach from making acid, which decreases heartburn.
Prilosec is not considered an antacid. There are other OTC drug products used to provide immediate relief for heartburn. These include antacids and acid reducer drug products such as Pepcid, Zantac, Tagamet, and Axid. Prilosec OTC should not be confused with these products because it works differently and is not intended for immediate relief.