What is a hiatus hernia?

The diaphragm is a muscle which partitions the body horizontally so that it divides the body cavity into chest and abdomen compartments. Everything above the diaphragm, by definition, is located in the chest. Everything below the diaphragm, by definition is located in the abdomen. Since the esophagus begins in the neck, passes through the chest, and enters the stomach in the abdomen, it must somehow pass through an opening in the diaphragm to get to the stomach. That opening is called the hiatus. When the support structures around the hiatus loosen up, the hiatus enlarges. In that instance, the upper part of the stomach may slide (herniated) up above the diaphragm and into the chest. The part of the stomach which has slid up into the chest is called a hiatus hernia. People with a hiatus hernia may or may not reflux. People who reflux may or may not have a hiatus hernia.