Heartburn, also known as pyrosis or acid indigestion is a burning sensation in the chest, just behind the breastbone or in the epigastrium. The pain often rises in the chest and may radiate to the neck, throat, or angle of the jaw.

Heartburn is usually associated with regurgitation of gastric acid (gastric reflux) which is the major symptom of gastroesophageal reflux disease (GERD). It however may also be a symptom of ischemic heart disease so concluding that it is gastroesophageal reflux disease prematurely may lead to misdiagnosis.

Heartburn can be caused by several conditions and a preliminary diagnosis of GERD is based on additional signs and symptoms. The chest pain caused by GERD has a distinct 'burning' sensation, occurs after eating or at night, and worsens when a person lies down or bends over. It also is common in pregnant women, and may be triggered by consuming food in large quantities, or specific foods containing certain spices, high fat content, or high acid content. If the chest pain is suspected to be heartburn, patients may undergo an upper GI series to confirm the presence of acid reflux. Heartburn or chest pain after eating or drinking and combined with difficulty swallowing may indicate esophageal spasms.