I'm not exactly sure, but I can tell you that when Plato was describing the location of the Tripartite soul and describing where reason lives was in the center of the chest. The Greeks didn't understand the relationship of brain to thought and thought the organs of the Torso were the center of all awareness. Aristotle when describing the different senses of the body uses the fact we feel hunger, sickness, the need relieve oneself and all those other non 5 sense functions the human body in the torso as proof of the necessary well being and understanding when something is not in balance. At some point I would conjecture when western society learned of the importance of the brain's relationship to thought, motor control, homeostatic functions whatever ephemeral things like emotions that that didn't understand got left in the old view of all our being being located in the chest.

The Greeks, at least in Homer, thought that the seat of the mind, compassion etc was located in the midriff, called the θυμός (thumos) although it is often translated as mind, spirit or a visceral need such as love or hunger. Hence phrases like "ἔπιον θ᾽ ὅσον ἤθελε θυμός" (The desire for eat and drink), "βαλέειν δέ ἑ θυμὸς ἀνώγει" (His heart urged him to shoot), "νεμεσίζεσθαι ἐνὶ θυμῷ" (He felt anger in his heart). These are all Homeric btw. But the point is that the seat of the mind and deep emotions like love were not located in the heart but somewhere near the diaphragm.

Not all societies use the heart for love. Iranians, I believe, think it's the liver.