In the West, the heart is the seat of the emotions. Here it's the hara (stomach).
A scheming man is a hara ni ichimotsu aru otoko (literally, "a man with an ulterior motive in his stomach"). A man's trusted friends are his fukushin (center of the stomach). People have dark stomachs (haraguroi) instead of dark hearts. When a person is angry the stomach stands up (hara ga tatsu). An injured mind takes its revenge with an act of haraise (soothing or healing the stomach). A serious decision is made with the belly (hara o kimeru). In lieu of heart-to-heart talks, we have hara o watta discussions, which literally "split open the stomach."
And if you really want to get graphic, there's harawata wa nashi (no intestines), a way of saying that there is no bad intention behind some careless or cruel remark.
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