'Heart' in the Bible

I pray that the eyes of your heart may be enlightened, so that you will know what is the hope of His calling, what are the riches of the glory of His inheritance in the saints,

Therefore I ask you not to lose heart at my tribulations on your behalf, for they are your glory.

being darkened in their understanding, excluded from the life of God because of the ignorance that is in them, because of the hardness of their heart;

speaking to one another in psalms and hymns and spiritual songs, singing and making melody with your heart to the Lord;

Slaves, be obedient to those who are your masters according to the flesh, with fear and trembling, in the sincerity of your heart, as to Christ;

not by way of eyeservice, as men-pleasers, but as slaves of Christ, doing the will of God from the heart.