Ancient Israelites offered the inner organs of sacrificial animals - entrails, kidneys, a portion of the liver. The heart is never mentioned. In all of the complicated sacrificial instructions of Leviticus, the word leb never appears, even once. We learn what happens to the stomach (Deuteronomy 18:3) but not the heart.

This is all the odder when we realize that the heart is often associated with one of the sacrificed organs - the kidneys (kilyah). Yahweh examines heart and kidneys (Psalm 7:9), tests the mind and heart (Psalm 26:2); when the Psalmist’s heart is embittered, it is as if something has pierced his kidneys (Psalm 73:21; cf. Jeremiah 17:10; 20:12).

And it is odd because the heart is so central to Hebraic anthropology. Out of it come the issues of life (Proverbs), and Israel is commanded to be devoted to Yahweh with the heart (Deuteronomy 6:5). What better way to  express this than to offer the heart ceremoniously into the altar fire?

Perhaps the heart is implied in the qereb, the “inner parts” that are placed on the altar (the “inner parts” and heart are juxtaposed in, e.g., Psalm 64:6). Even so, why not make it explicit?

No theories here. Only questions.