Achalasia of the oesophagus. Endoscopic view of a closed sphincter in the oesophagus of a patient affected by achalasia. Achalasia is a failure of smooth muscle fibres to relax, which can cause the lower oesophageal sphincter to remain closed (as here). It can happen at various points along the gastrointestinal tract. Oesophageal achalasia can cause difficulty in swallowing, regurgitation and sometimes chest pain. It often has no underlying cause. Treatment with drugs often causes relief.