The word “heart” has a very long history. In Old English it is heorte, of Germanic origin; related to Dutch hart and German Herz, and comes from an Indo-European root shared by Latin cor, cord- and Greek ker, kardia. Its meaning relates to the centre or “core” of something: you call the centre of an apple its “core,” the centre of a cabbage is its “heart” – same thing, different modern words. The painful sensation in the centre of the chest one gets from acid present in the lower end of the oesophagus is described as “burning” when the cause is known. (spelled “esophagus” -if quota’s spell checker will relent, that is an initial “e” not an “oe”in American English).
The exact same sensation in the same place is described as just plain “pain” if it is known to be the result of damage due to shortage of blood flow through heart muscle. The sensation that results from effort induced shortage of blood flow through the heart’s narrowed supply arteries (coronary arteries) without infarction is different. It has a component of difficulty in breathing and pain, and is called angina pectoris – “clenching, clenching, narrowing or gripping of the chest.”
Pain sensation in organs such as the heart, stomach and oesophagus is poorly localised. Regardless of the origin it is felt in the centre. So it refers to heart in the sense of the centre and not the organ. In fact the organ is named “the heart” for its location – occupying the centre of the chest. Even in Latin, the organ is called cor, which means centre (and compare the French coeur). The first part of the stomach is called the Cardia from the Greek, k-ardia (that spell-checker again!) also meaning centre. The stomach occupies the centre of the abdomen.
The word burn is derived from a combination of Old Norse brenna “to burn, light,” and two originally distinct Old English verbs: brnan “to kindle” and beornan “to be on fire”, all from Proto-Germanic *brennan/branajan (cf. Middle Dutch bernen, Modern Dutch branden, Old High German brinnan, German brennen, Gothic -brannjan “to set on fire”). The severe deep-seated pain caused by being burnt was well known to our ancestors.
I am confident the word heartburn was in use for the concept of pain due to bad digestion (indigestion,) from eating too much, or difficult to digest or even spoiled food, for many centuries before the importance of distinguishing between it and a myocardial infarction was realised only comparatively recently.
Heartburn simply means “pain in the centre, low down in the chest or high up in the abdomen or both.” Correctly, it has nothing to do with the organ called “the heart.”
This answer originally appeared on this Quora question on Acid Reflux.