true feelings; real intention; one's heart
Refers to what someone genuinely thinks or feels, often contrasted with outward words or behavior. Common in expressions like 本心を言う, 本心を見せる, or 本心かどうか.
I don't know if his words reflect his true feelings.
なかなか本心を見せない人だ。
He's someone who rarely shows his real intentions.
right mind; senses; conscience
Used in set phrases like 本心に返る (come to one's senses) or 本心を失う (lose one's right mind). This usage is somewhat literary or formal.
彼はようやく本心に返った。
He finally came to his senses.
怒りで本心を失ってはいけない。
You must not lose your right mind in anger.
He finally told me how he really felt.
She hid her true feelings behind a smile.
He rarely shows his true feelings.
I can't tell what that person really thinks.
I'm truly grateful, from the heart.
After a while, he came to his senses.
本心 refers to one's true, unmasked intentions or feelings as opposed to a facade, while 胸中 more broadly covers whatever one is currently thinking or feeling inside.
本心 refers to one's true feelings or real intention, often contrasted with outward behavior, whereas 衷心 emphasizes deep, sincere emotion itself.