The esophagus passes through a muscle, called the diaphragm, which separates the lungs from the abdomen. When the opening in the diaphragm enlarges, a portion of the stomach can protrude (herniate) through it into the chest. This is called a hiatal hernia. A persistent hiatal hernia may produce significant heartburn. Many people with a hiatus hernia do not experience heartburn. However, 40-50% of patients with a hiatal hernia have reflux. A hiatal hernia and GERD can occur independently from one another.