The document discusses how heartburn is caused by imbalanced gastric juices or acids in the stomach, and that antacids are medications that help correct the pH balance in the stomach. It begins to explain that the pH scale measures acidity and alkalinity, ranging from 0-14, with lower numbers being more acidic and higher numbers being more basic or alkaline. The document appears to be setting up to discuss the effect of heartburn on the stomach in relation to pH levels.