So whoever Allah wants to guide - He expands his breast to (6:125)

﴿فَمَن يُرِدِ اللَّهُ أَن يَهْدِيَهُ يَشْرَحْ صَدْرَهُ لِلْإِسْلَامِ ۖ وَمَن يُرِدْ أَن يُضِلَّهُ يَجْعَلْ صَدْرَهُ ضَيِّقًا حَرَجًا كَأَنَّمَا يَصَّعَّدُ فِي السَّمَاءِ ۚ كَذَٰلِكَ يَجْعَلُ اللَّهُ الرِّجْسَ عَلَى الَّذِينَ لَا يُؤْمِنُونَ﴾
[ الأنعام: 125]

6:125 So whoever Allah wants to guide - He expands his breast to [contain] Islam; and whoever He wants to misguide - He makes his breast tight and constricted as though he were climbing into the sky. Thus does Allah place defilement upon those who do not believe.

Whomever Allah wishes to guide to the right path, He opens their heart to Islam so they accept it willingly.
Whomever He wishes to abandon and not guide, He makes their chest extremely narrow and unable to accept the truth, such that they become like a person climbing into the higher layers of the atmosphere while finding it increasingly difficult to breathe.
Just as Allah made this extreme narrowness the condition of the person who goes astray, He will place the punishment on those who do not have faith in Him.

And whomsoever Allah wills to guide, He opens his breast to Islam, and whomsoever He wills to send astray, He makes his breast closed and constricted, as if he is climbing up to the sky. Thus Allah puts the wrath on those who believe not.

phonetic Transliteration

Faman yuridi Allahu an yahdiyahu yashrah sadrahu lilislami waman yurid an yudillahu yajAAal sadrahu dayyiqan harajan kaannama yassaAAAAadu fee alssamai kathalika yajAAalu Allahu alrrijsa AAala allatheena la yuminoona

Abdullah Yusuf Ali - Translation

Those whom Allah (in His plan) willeth to guide,- He openeth their breast to Islam; those whom He willeth to leave straying,- He maketh their breast close and constricted, as if they had to climb up to the skies: thus doth Allah (heap) the penalty on those who refuse to believe.

Safi-ur-Rahman al-Mubarakpuri

And whomsoever Allah wills to guide, He opens his breast to Islam; and whomsoever He wills to send astray, He makes his breast closed and constricted, as if he is climbing up to the sky. Thus Allah puts the wrath on those who believe not.

Page 144 English transliteration