Heartburn is a burning sensation felt behind the breastbone. It is a symptom that is commonly linked to acid reflux and is often triggered by food. Lying down, bending, lifting, and performing certain exercises can exacerbate heartburn. Causes include acid reflux, gastroesophageal reflux disease (GERD), damage to the esophageal lining, bile acid, mechanical stimulation to the esophagus, and esophageal hypersensitivity. Heartburn affects 25% of the population at least once a month.

Endoscopy and esophageal pH monitoring can be used to evaluate heartburn. Some causes of heartburn, such as GERD, may be diagnosed based on symptoms alone. Potential differential diagnoses for heartburn include motility disorders, ulcers, inflammation of the esophagus, and medication side effects. Lifestyle changes, such as losing weight and avoiding fatty foods, can improve heartburn. Over-the-counter alginates or antacids can help with mild or occasional heartburn. Heartburn treatment primarily involves antisecretory medications like H2 receptor antagonists (H2RAs) and proton-pump inhibitors (PPIs).

Heartburn is a burning sensation felt behind the breastbone, rising to the throat, and may be associated with an acidic taste. Heartburn is often associated with acid reflux or regurgitation. It is sometimes referred to as indigestion, sour stomach, acid regurgitation, or bitter belching. Heartburn is considered troublesome if mild symptoms occur two or more days a week, or moderate/severe symptoms are present at least once per week.

The sensation of heartburn often spreads to the neck, throat, or back and is commonly triggered by food. It tends to occur within an hour after eating, especially after a large meal. Lying down, especially after eating, can make heartburn worse. Some people find their symptoms more severe when lying on their right side. Nightime heartburn can disrupt sleep and affect daily life. Activities that increase abdominal pressure, like bending, lifting heavy objects, or performing certain exercises, can also trigger symptoms. Studies suggest that stress and lack of sleep may make heartburn feel worse by increasing the body's sensitivity to symptoms.

The differential diagnosis, a process used by healthcare professionals to help differentiate a diagnosis from other similar disorders, for heartburn includes motility disorders such as achalasia and gastroparesis; peptic ulcers; functional dyspepsia; angina; eosinophilic esophagitis; coronary artery disease; functional heartburn; peristalsis; acid reflux; inflammation of the esophagus (esophagitis), stomach (gastritis), pancreas (pancreatitis), gallbladder (cholecystitis), and duodenum (duodenitis); esophageal cancer; ischemic pain; hiatal hernia; biliary colic; stomach cancer; gallstones; pancreatic cancer; duodenal ulcer; and mesenteric adenitis. Heartburn can also be caused by certain medications such as nonsteroidal anti‐inflammatory drugs, corticosteroids, tetracycline antibiotics, bisphosphonates, calcium‐channel blockers, nitrates, tricyclic antidepressants, and anticholinergics.

The exact causes of heartburn are not fully understood, but they likely involve multiple factors, including chemical irritation, pressure on the esophagus, and increased sensitivity to pain.

Acid reflux is a common cause of heartburn but is not the only etiology. A study in 1989 demonstrated this by giving participants acidic and basic solutions; the acidic solutions induced heartburn in all participants, though the more basic solution still invoked heartburn in over 40% of the participants. Ambulatory pH monitoring reveals that just a small percentage of acid reflux episodes trigger heartburn.

Nerve endings and acid-sensitive ion channels in the deepest layer of the esophagus are usually protected by anatomical barriers. However, in gastroesophageal reflux disease (GERD), one of the earliest signs of damage is the development of dilated intercellular spaces (DISs) in the esophageal lining. These spaces weaken the protective barrier, allowing acid and other substances to seep in. This triggers pain-sensitive nerves, which send signals to the brain and cause the sensation of heartburn.