'Heart' in the Bible

Wherefore I was wroth with this generation, and said, They always err in heart; and they have not known my ways;

See, brethren, lest there be in any one of you a wicked heart of unbelief, in turning away from the living God.

For the word of God is living and operative, and sharper than any two-edged sword, and penetrating to the division of soul and spirit, both of joints and marrow, and a discerner of the thoughts and intents of the heart.

let us approach with a true heart, in full assurance of faith, sprinkled as to our hearts from a wicked conscience, and washed as to our body with pure water.

Be not carried away with various and strange doctrines; for it is good that the heart be confirmed with grace, not meats; those who have walked in which have not been profited by them.