'Heart' in the Bible

I give praise to God, whose servant I have been, with a heart free from sin, from the time of my fathers, because in my prayers at all times the thought of you is with me, night and day

But keep yourself from those desires of the flesh which are strong when the body is young, and go after righteousness, faith, love, peace, with those whose prayers go up to the Lord from a clean heart.

Gently guiding those who go against the teaching; if by chance God may give them a change of heart and true knowledge,