Heart
The 'heart' in this chapter symbolizes the inner spiritual condition and devotion of the kings, particularly Abijam and Asa, towards God.
The heart represents the sincerity and faithfulness of one's relationship with God. Abijam's heart was not fully devoted to the Lord, unlike David, while Asa's heart was fully committed to the Lord all his life.
In ancient Hebrew culture, the heart was seen as the center of thought, emotion, and moral decision-making.