The word(s) "hearts" appears 130 time(s) in 121 verse(s) in Quran in Muhammad Pickthal translation.

(11) Allah ordained this only as a message of good cheer for you, and that thereby your hearts might be at rest - Victory cometh only from Allah, the Mighty, the Wise -

(12) We shall cast terror into the hearts of those who disbelieve because they ascribe unto Allah partners, for which no warrant hath been revealed. Their habitation is the Fire, and hapless the abode of the wrong-doers.

(13) Then, after grief, He sent down security for you. As slumber did it overcome a party of you, while (the other) party, who were anxious on their own account, thought wrongly of Allah, the thought of ignorance. They said: Have we any part in the cause? Say (O Muhammad): The cause belongeth wholly to Allah. They hide within themselves (a thought) which they reveal not unto thee, saying: Had we had any part in the cause we should not have been slain here. Say: Even though ye had been in your houses, those appointed to be slain would have gone forth to the places where they were to lie. (All this hath been) in order that Allah might try what is in your breasts and prove what is in your hearts. Allah is Aware of what is hidden in the breasts (of men).

(14) O ye who believe! Be not as those who disbelieved and said of their brethren who went abroad in the land or were fighting in the field: If they had been (here) with us they would not have died or been killed: that Allah may make it anguish in their hearts. Allah giveth life and causeth death; and Allah is Seer of what ye do.

(15) And that He might know the hypocrites, unto whom it was said: Come, fight in the way of Allah, or defend yourselves. They answered: If we knew aught of fighting we would follow you. On that day they were nearer disbelief than faith. They utter with their mouths a thing which is not in their hearts. Allah is Best Aware of what they hide.

(16) Those are they, the secrets of whose hearts Allah knoweth. So oppose them and admonish them, and address them in plain terms about their souls.

(17) Except those who seek refuge with a people between whom and you there is a covenant, or (those who) come unto you because their hearts forbid them to make war on you or make war on their own folk. Had Allah willed He could have given them power over you so that assuredly they would have fought you. So, if they hold aloof from you and wage not war against you and offer you peace, Allah alloweth you no way against them.

(18) Then because of their breaking of their covenant, and their disbelieving in the revelations of Allah, and their slaying of the prophets wrongfully, and their saying: Our hearts are hardened - Nay, but Allah set a seal upon them for their disbelief, so that they believe not save a few -

(19) And because of their breaking their covenant, We have cursed them and made hard their hearts. They change words from their context and forget a part of that whereof they were admonished. Thou wilt not cease to discover treachery from all save a few of them. But bear with them and pardon them. Lo! Allah loveth the kindly.

(20) O Messenger! Let not them grieve thee who vie one with another in the race to disbelief, of such as say with their mouths: "We believe," but their hearts believe not, and of the Jews: listeners for the sake of falsehood, listeners on behalf of other folk who come not unto thee, changing words from their context and saying: If this be given unto you, receive it, but if this be not given unto you, then beware! He whom Allah doometh unto sin, thou (by thine efforts) wilt avail him naught against Allah. Those are they for whom the Will of Allah is that He cleanse not their hearts. Theirs in the world will be ignominy, and in the Hereafter an awful doom;