Achalasia is a disorder of the esophagus where the muscle at the end of the esophagus does not relax enough to allow food to move properly into the stomach. Achalasia prevents food and liquids from moving into the stomach from the esophagus. The lower esophageal sphincter (LES) is a muscular ring. It relaxes (opens) during swallowing. With achalasia, it does not relax. Also with achalasia, peristalsis does not work well. This is the normal action of the esophagus that moves food into the stomach.
For more detailed information, please visit the Society of Thoracic Surgeons.