at heart 内心里，本质上

【例句】
He was a kid at heart who never really grew up.
迈克尔的内心深处住着一个永远也长不大的小男孩。

It knows what it's talking about and it has your best interests at heart.
它知道它说的是什么，而且它知道你内心深处的兴趣是什么。