The main reason you experience the pain of heartburn is that stomach acid is backing up into your esophagus and burning the delicate tissues there.
Beyond this though there are other, underlying causes for heartburn that you may have control over; you may even be able to use that control plus a little knowledge to stop the pain.

• Food: There are certain foods that commonly cause heartburn pain in some people.
  You have to be your own detective to figure out which ones may be a problem for you.
  Citrus foods such as oranges, tomatoes, and tomato sauce as well as raw onions can irritate the esophagus as they go down.
  If the tissues are already irritated by stomach acid, this can be very painful.
  Some meat, such as beef, can take up to 10 hours to digest which increases the amount of stomach acid present and leaves more time for it to back up and harm you.
  Milk, which feels good going down and used to be prescribed for ulcers, actually creates more acid once it's in your stomach.
  These are just a few of the foods to avoid that may be causing you difficulty.
  There are also foods you can eat to relieve heartburn symptoms!
• Too Little Stomach Acid: Believe it or not, some people don't create enough stomach acid and this creates heartburn pain of its own.
  It also makes it difficult for your body to digest protein and can cause mineral deficiencies.
  One teaspoon to a tablespoon of organic apple cider vinegar in water before meals is good for this condition as well as for those with too much acid.
  
• Exercise: Any type of exercise which causes the stomach acid to bounce around and up into the esophagus has the potential for causing heartburn.
  Jogging and biking are included on the list, but so are sports like weight lifting which involve straining, tightening of the muscles of the abdomen and squeezing of the stomach.
  If you exercise before you eat, you'll have less chance of experiencing heartburn.
  
• Pregnancy: When you're pregnant, two things happen at once.
  Hormones cause the LES (the sphincter that keeps the stomach acid in the stomach) to relax and allow stomach acid to move into the esophagus and at the same time, the developing fetus puts more and more pressure on the stomach and other internal organs.
  Eating smaller meals and wearing looser clothing may help.
  Also, avoid lying down after you eat.
  
• Medication: If you take medicine for other conditions, one of the side effects may be heartburn.
  Talk with your doctor to see if you can change to a medication that doesn't have this effect.
  
• Weight: If you're overweight, the extra body mass puts pressure on your stomach and LES.
  Eating smaller meals may alleviate some of this pressure.
  Of course, losing weight will improve your situation.
  
• Smoking: Chemicals in smoke can relax the LES and create the environment for heartburn to occur.
  
• Alcohol: Some people with heartburn can enjoy a glass of beer or wine sipped slowly with food.
  However, alcohol is another substance that relaxes the LES, so cutting back may be your only option if you experience heartburn when you drink.
  
• Candida and Parasites: Candida is a yeast infection that can become a serious problem in your system.
  It occurs naturally in most people and in the right quantities is not a threat and can even be helpful.
  However, when yeast becomes overgrown, the list of symptoms it causes is truly horrific.
  Among these is heartburn.
  Parasites are organisms that can live in your digestive tract.
  They can be picked up in food or unclean water or from pets or farm animals.
  Parasites cause major digestive disturbances including heartburn.
  There are simple tests you can take to determine if yeast or parasites are causing your heartburn symptoms.
  

These are a few (out of a list of over 100!) causes of heartburn.