left breast; left side of the chest
Refers to the left chest area, often in contexts of pain, clothing, or where the heart is located.
左胸に痛みを感じる。
I feel a pain in my left chest.
彼は左胸に手を当てた。
He put his hand on his left chest.
Compound of 左 (ひだり, 'left') and 胸 (むね, 'chest').