Fetching details from the dictionary...
true feelings; real intention; one's heart
one's right mind; one's senses; one's conscience
友人に本心を打ち明けた。
I opened up about my true feelings to a friend.
本心では賛成していないようだ。
It seems he doesn't truly agree.
人の本心は言葉だけでは判断できない。
You cannot judge a person's true feelings by words alone.