This condition is more common than you'd think.  In my work with eating disorders it's a frequent complication of the illness, especially for those who struggle with purging.

Let's talk basic anatomy.  Heartburn is the common word for gastroesophageal reflux.  Gastro = stomach, esophageal = esophagus (the tube that connects your mouth to stomach), reflux = stomach acid comes back up from the stomach to the esophagus.

When the acid is moving from the stomach to the esophagus, it's going the wrong way.  There's a flap that separates your stomach and esophagus that is designed to allow food to go down and stay down (sort of like the flap in your sink for the garbage disposal).  Sometimes the contents of the stomach leak back up, especially if the flap gets weakened.  The reason it feels like burning in your chest (hence the name heartburn) is because the contents in your stomach are mixed with stomach acid, and the acid burns. 

Luckily your stomach is coated with a protective mucus that prevents the stomach from the acid, but your esophagus doesn't have that protection.  Thus, the stomach acid is very hard on your esophagus, especially when this is happening repeatedly.  So besides it being an annoying condition (nobody likes the burning sensation in their chest), it can also produce further damage to the esophagus.

Food doesn't cause heartburn, although certain foods can exacerbate it. Here are some foods to limit or avoid if you have heartburn:

• Acidic foods (e.g. citrus fruits, tomatoes and tomato products, soda)
• Spicy foods
• Caffeine
• Alcohol
• Chocolate
• Eat small, frequent meals to avoid overfilling of the stomach

You should also avoid lying down for about 45-60 minutes after eating to allow the food to pass through your stomach into your small intestine.  You can try sleeping with your head/torso elevated with extra pillows too. 

Also, your doctor may suggest medication to help manage the reflux, and in certain scenarios surgery is possible.