'Heart' in the Bible

Therefore I was greatly grieved with that generation, and I said, 'They are ever going astray in heart, and have not learnt to know My paths.'

see to it, brethren, that there is never in any one of you--as perhaps there may be--a sinful and unbelieving heart, manifesting itself in revolt from the ever-living God.

For God's Message is full of life and power, and is keener than the sharpest two-edged sword. It pierces even to the severance of soul from spirit, and penetrates between the joints and the marrow, and it can discern the secret thoughts and purposes of the heart.

Do not be drawn aside by all sorts of strange teaching; for it is well to have the heart made stedfast through God's grace, and not by special kinds of food, from which those who scrupulously attend to them have derived no benefit.