• 胸中きょうちゅう — one’s heart; inner feelings
• 胸部きょうぶ — chest region
• 胸むねが痛いたむ — to feel pain in one’s chest (emotionally)
• 胸騒むなさわぎ — premonition; uneasy feeling
• 胸囲きょうい — chest measurement
• 胸焼むねやけ — heartburn

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Built from the body radical ⺼ (meat/flesh) and the phonetic component 旨, 胸 points to the area that “holds” vital organs (heart/lungs) and, by extension, one’s feelings or resolve.

胸むねが 苦くるしくなった。
I felt tightness in my chest.

胸中きょうちゅうを 語かたる。
To speak about one’s inner thoughts.