How can you tell if you have hiatial hernia or gerd? what are the differences?

Hiatal hernia is when the upper part of the stomach moves up through the opening into the chest area. Gerd is when the contents of the stomach can go up through an incompetent valve in to the esophagus (tube taking food down to the stomach). You can tell the difference by x-ray tests and endoscopy (looking into the tube and stomach) by a special instrument.