Weybe Subway

The food ingested travels through esophagus to the stomach, which is tightly closed by lower esophageal sphincter allowing ingested food entry only of the, preventing its reverse movement from stomach to esophagus. The symptoms of sodbrennen are felt in esophagus when the food undergoing digestion mixed with acidic gastric juice in the stomach finds back entry into the esophagus.
 
The gastric wall has protection from gastric acid acting on it due to a mucus layer, whereas the esophagus wall lacks presence of protective mucus layer. Hence the acid present mixed with food reaching esophagus causes burning sensation. Since its location is in the chest it is also referred to as heartburn. The heart organ is not at all involved in it. 
In case there is improper closure of esophagus by lower esophageal sphincter, the food from stomach reaches back to esophagus causing heart burn and there is likelihood of esophagus getting damaged and if condition is not checked, it progresses further to ulcer formation later on.