Achalasia is a swallowing disorder (dysphagia) that results from the inability of the muscular ring at the lower end of the esophagus (lower esophageal sphincter - LES) to relax, and the lack of coordinated movement of the esophageal muscles (loss of peristalsis). In a healthy individual, swallowed food is propelled towards the stomach by the rhythmic contractions of the esophageal muscles (peristalsis). The LES, located where the esophagus joins the stomach, relaxes during swallowing, allowing food to pass into the stomach and preventing its backflow. In patients with achalasia, this natural process is disrupted due to damage to the nerve cells in the esophagus. While the LES fails to relax adequately, the contractile movements of the esophagus also cannot occur effectively. This condition prevents the passage of solid and liquid foods into the stomach, leading to their accumulation in the esophagus. Over time, the esophagus may dilate, and fermented food accumulated inside may return to the mouth with a bitter taste (regurgitation).