The word(s) "hearts" appears 132 time(s) in 121 verse(s) in Quran in Mohsin Khan translation.

(1) Allah has set a seal on their hearts and on their hearing, (i.e. they are closed from accepting Allah's Guidance), and on their eyes there is a covering. Theirs will be a great torment.

(2) In their hearts is a disease (of doubt and hypocrisy) and Allah has increased their disease. A painful torment is theirs because they used to tell lies.

(3) Then, after that, your hearts were hardened and became as stones or even worse in hardness. And indeed, there are stones out of which rivers gush forth, and indeed, there are of them (stones) which split asunder so that water flows from them, and indeed, there are of them (stones) which fall down for fear of Allah. And Allah is not unaware of what you do.

(4) And they say, "Our hearts are wrapped (i.e. do not hear or understand Allah's Word)." Nay, Allah has cursed them for their disbelief, so little is that which they believe.

(5) And (remember) when We took your covenant and We raised above you the Mount (saying), "Hold firmly to what We have given you and hear (Our Word)." They said, "We have heard and disobeyed." And their hearts absorbed (the worship of) the calf because of their disbelief. Say: "Worst indeed is that which your faith enjoins on you if you are believers."

(6) And those who have no knowledge say: "Why does not Allah speak to us (face to face) or why does not a sign come to us?" So said the people before them words of similar import. Their hearts are alike, We have indeed made plain the signs for people who believe with certainty.

(7) Allah will not call you to account for that which is unintentional in your oaths, but He will call you to account for that which your hearts have earned. And Allah is Oft-Forgiving, Most-Forbearing.

(8) It is He Who has sent down to you (Muhammad صلى الله عليه وسلم) the Book (this Qur'an). In it are Verses that are entirely clear, they are the foundations of the Book [and those are the Verses of Al-Ahkam (commandments), Al-Fara'id (obligatory duties) and Al-Hudud (legal laws for the punishment of thieves, adulterers)]; and others not entirely clear. So as for those in whose hearts there is a deviation (from the truth) they follow that which is not entirely clear thereof, seeking Al-Fitnah (polytheism and trials), and seeking for its hidden meanings, but none knows its hidden meanings save Allah. And those who are firmly grounded in knowledge say: "We believe in it; the whole of it (clear and unclear Verses) are from our Lord." And none receive admonition except men of understanding. (Tafsir At-Tabari).

(9) (They say): "Our Lord! Let not our hearts deviate (from the truth) after You have guided us, and grant us mercy from You. Truly, You are the Bestower."

(10) Verily, those who disbelieved after their Belief and then went on increasing in their disbelief (i.e. disbelief in the Qur'an and in Prophet Muhammad صلى الله عليه وسلم) - never will their repentance be accepted [because they repent only by their tongues and not from their hearts]. And they are those who are astray.