Heartburn, the main symptom of gastrooesophageal reflux disease (GORD), might be expected to occur infrequently in achalasia, a disorder characterised by a hypertensive lower oesophageal sphincter (LOS) that fails to relax. Nevertheless, it is often described by patients with achalasia. The medical records of 32 patients with untreated achalasia who complained of heartburn, and of 35 similar patients who denied the symptom, were reviewed to explore the implications of heartburn in this condition. Data on endoscopic and manometric findings, and on the onset and duration of oesophageal symptoms were collected. Three patterns of heartburn were observed: (1) in 8 patients (25%) the onset of heartburn followed the onset of dysphagia, (2) in 15 patients (47%) heartburn preceded the onset of dysphagia and persisted as dysphagia progressed, and (3) in 9 patients (28%), heartburn preceded the onset of dysphagia and stopped as dysphagia progressed. The mean (SD) basal LOS pressure in the patients with heartburn (38 (16) mm Hg) was significantly lower than that in patients without the symptom (52 (26) mm Hg); the lowest LOS pressure (29 (11) mm Hg) was observed in the subset of patients whose heartburn preceded the onset of dysphagia and then stopped. It is concluded that patients who have achalasia with heartburn have lower basal LOS pressures than patients who have achalasia without this symptom. In some patients with achalasia, the appearance of dysphagia is heralded by the disappearance of longstanding heartburn. For these patients, it is speculated that achalasia develops in the setting of underlying GORD.