The word(s) "heart" appears 171 time(s) in 159 verse(s) in Quran in Muhammad Habib Shakir translation.

(21) O you who believe! be not like those who disbelieve and say of their brethren when they travel in the earth or engage in fighting: Had they been with us, they would not have died and they would not have been slain; so Allah makes this to be an intense regret in their hearts; and Allah gives life and causes death and Allah sees what you do.

(22) Thus it is due to mercy from Allah that you deal with them gently, and had you been rough, hard hearted, they would certainly have dispersed from around you; pardon them therefore and ask pardon for them, and take counsel with them in the affair; so when you have decided, then place your trust in Allah; surely Allah loves those who trust.

(23) And that He might know the hypocrites; and it was said to them: Come, fight in Allah's way, or defend yourselves. They said: If we knew fighting, we would certainly have followed you. They were on that day much nearer to unbelief than to belief. They say with their mouths what is not in their hearts, and Allah best knows what they conceal.

(24) These are they of whom Allah knows what is in their hearts; therefore turn aside from them and admonish them, and speak to them effectual words concerning themselves.

(25) But no! by your Lord! they do not believe (in reality) until they make you a judge of that which has become a matter of disagreement among them, and then do not find any straitness in their hearts as to what you have decided and submit with entire submission.

(26) Except those who reach a people between whom and you there is an alliance, or who come to you, their hearts shrinking from fighting you or fighting their own people; and if Allah had pleased, He would have given them power over you, so that they should have certainly fought you; therefore if they withdraw from you and do not fight you and offer you peace, then Allah has not given you a way against them.

(27) And be not weak hearted in pursuit of the enemy; if you suffer pain, then surely they (too) suffer pain as you suffer pain, and you hope from Allah what they do not hope; and Allah is Knowing, Wise.

(28) Therefore, for their breaking their covenant and their disbelief in the communications of Allah and their killing the prophets wrongfully and their saying: Our hearts are covered; nay! Allah set a seal upon them owing to their unbelief, so they shall not believe except a few.

(29) But on account of their breaking their covenant We cursed them and made their hearts hard; they altered the words from their places and they neglected a portion of what they were reminded of; and you shall always discover treachery in them excepting a few of them; so pardon them and turn away; surely Allah loves those who do good (to others).

(30) O Apostle! let not those grieve you who strive together in hastening to unbelief from among those who say with their mouths: We believe, and their hearts do not believe, and from among those who are Jews; they are listeners for the sake of a lie, listeners for another people who have not come to you; they alter the words from their places, saying: If you are given this, take it, and if you are not given this, be cautious; and as for him whose temptation Allah desires, you cannot control anything for him with Allah. Those are they for whom Allah does not desire that He should purify their hearts; they shall have disgrace in this world, and they shall have a grievous chastisement in the hereafter.