'Hearts' in the Bible

Their hearts overflowed with all sorts of dishonesty, mischief, greed, malice. They were full of envy and murder, and were quarrelsome, crafty, and spiteful.

since they exhibit proof that a knowledge of the conduct which the Law requires is engraven on their hearts, while their consciences also bear witness to the Law, and their thoughts, as if in mutual discussion, accuse them or perhaps maintain their innocence--

and that this hope never disappoints, because God's love for us floods our hearts through the Holy Spirit who has been given to us.

And those whose hearts are absorbed in earthly things cannot please God.

and the Searcher of hearts knows what the Spirit's meaning is, because His intercessions for God's people are in harmony with God's will.