Achalasia
（重定向自Achalasia of the Cardia）
Achalasia (/eɪkəˈleɪʒə/; a- + -chalasia "no relaxation") is a failure of smooth muscle fibers to relax, which can cause a sphincter to remain closed and fail to open when needed. Without a modifier, "achalasia" usually refers to achalasia of the esophagus, which is also called esophageal achalasia, achalasia cardiae, cardiospasm, and esophageal aperistalsis. Achalasia can happen at various points along the gastrointestinal tract; achalasia of the rectum, for instance, in Hirschsprung's disease.