'Heart' in the Bible

He who says that he is in the light, and has hate in his heart for his brother, is still in the dark.

But if a man has this world's goods, and sees that his brother is in need, and keeps his heart shut against his brother, how is it possible for the love of God to be in him?

In this way we may be certain that we are true, and may give our heart comfort before him,

When our heart says that we have done wrong; because God is greater than our heart, and has knowledge of all things.

My loved ones, if our heart does not say that we have done wrong, we have no fear before him;