A hiatus hernia occurs when a part of the stomach pushes through the diaphragm into the chest cavity. The diaphragm is a muscle that separates the chest from the abdomen and helps with breathing. This condition can lead to symptoms like heartburn, chest pain, and difficulty swallowing. There are two main types of hiatus hernias: sliding and paraesophageal. A sliding hernia is the most common type, where the stomach and part of the esophagus slide up and down through the hiatus. A paraesophageal hernia is less common but can be more serious, as it may cause the stomach to become trapped.