expression
brazen-faced; shameless; thick-skinned
Idiomatic expression describing someone who is utterly shameless or audacious, as if their heart were covered in hair. Often used in a critical or exasperated tone.
あんな嘘をつくなんて、心臓に毛が生えたやつだ。
Telling a lie like that—what a brazen-faced guy.
彼女は心臓に毛が生えたように平然としていた。
She remained completely unruffled, as if she had no shame at all.
The phrase literally means 'hair has grown on one's heart', implying a heart so calloused or insensitive that it grows hair, hence a person is shameless or brazen. The exact origin is uncertain, but it is a well-established Japanese idiom.