'Heart' in the Bible

-- since the eyes of your heart have been enlightened -- so that you may know what is the hope of his calling, what is the wealth of his glorious inheritance in the saints,

For this reason I ask you not to lose heart because of what I am suffering for you, which is your glory.

Slaves, obey your human masters with fear and trembling, in the sincerity of your heart as to Christ,

not like those who do their work only when someone is watching -- as people-pleasers -- but as slaves of Christ doing the will of God from the heart.