The lower esophagus ends at the LES, where the leaves of the diaphragm close it to prevent reflux.
If there is a weakness of this area, a hernia may occur, allowing the stomach up into the chest. Sometimes very far.
Failure of medication and proof of reflux vith a pH monitor, may require surgery.
A thoracic surgery used to be standard, but now a Nissen fundoplication is the most definitive treatment.