胸が裂ける (mune ga sakeru: to feel strong grief) heart + to burst
胸が空く (mune ga suku: to have no worries) heart + to empty out
胸が潰れる (mune ga tsubureru: to be shocked, have a terrible surprise) heart + to stop functioning
The breakdown brings to mind the English expression, “I nearly had a heart attack when I heard the news.” The second kanji here is non-Jōyō. I hope that doesn’t come as a terrible shock!
胸が塞がる (mune ga fusagaru: to be depressed) heart + to be clogged
Fascinating breakdown! We’ve seen the second kanji (which is non-Jōyō) in 塞ぎ込む (fusagikomu: to mope, get depressed, to obstruct + to move inward).
胸を撫で下ろす (mune o nadeorosu: to feel relieved)
heart + to stroke down (last 2 chars.)
In 撫で下ろす, the first kanji is non-Jōyō and means “to stroke, pat, smooth down.” The second kanji means “down.” So if you’re feeling relieved, it’s as if someone is giving your heart a good petting!