The Heart
The heart is a commonly used phrase throughout the Bible.  Therefore, it is worth studying the verses which mention the matter of the heart to see the context and meaning for such a term.

In general the heart is composed of four aspects of our being:  the mind, emotion and will (of the soul) and the conscience (of the spirit).

mind

Matthew 9:4

Hebrews 4:12

Genesis 6:5

will

Acts 11:23

Hebrews 4:12

emotion

John 16:22

conscience

Hebrews 10:22

1 John 3:20