The diaphragm is the muscular wall that separates the chest from the abdomen. The hiatus is a small muscular collar in the diaphragm, through which the esophagus, or swallowing tube, passes to connect the mouth to the stomach. A hiatal hernia occurs when the top part of the stomach protrudes through the muscular collar and into the chest. It is very common and may exist in more than 40 percent of the population.
Many cases even go unnoticed.
If the muscular collar is too large or relaxes, a sliding hiatal hernia may occur. Obesity, pregnancy, tight clothing, and movement like bending, coughing, or straining can create the pressure that causes the sliding. Often there are no symptoms or only a sense of heartburn or fullness in the chest after eating. For people who experience heartburn and belching symptoms, an additional problem exists that is called gastroesophageal reflux. This is the backflow of acid contents of the stomach into the esophagus.