noun
lungs; bottom of one's heart; vital point
Literally 'lungs', but more often used figuratively in expressions like 肺腑をえぐる (to pierce one's heart) or 肺腑にしみる (to sink deep into one's heart). The figurative sense emphasizes deep emotional impact or the core of one's being.
彼の言葉は私の肺腑をえぐった。
His words pierced my heart.
その美しい旋律が肺腑にしみた。
The beautiful melody sank deep into my heart.