Gastroenterology Consultants,SC: Diseases of the GI tract HIATUS HERNIA [<<back | list all>>] The diaphragm is a sheet of muscle that separates the lungs from the abdomen. When a person takes a deep breath, the dome-shaped diaphragm contracts and flattens. In doing this the diaphragm pulls air into the lungs. The left diaphragm contains a small hole through which passes the tube-shaped esophagus that carries food and liquid to the stomach. Normally this hole, called a hiatus, is small and fits snugly around the esophagus. The J-shaped stomach sits below the diaphragm. In some people, the hiatus or hole in the diaphragm weakens and enlarges. It is not known why this occurs. When a portion of the stomach herniates, or moves up, into the chest cavity through this enlarged hole, a hiatus hernia is now present.