详细解释:在内心里
词意辨析：
at heart, by heart这是两个与heart有关的词组。
at heart: 意思是“在心里”、“心底里”或“本质上”（from the heart，from the bottom of one's heart or essentially）。that socialite is a rascal at heart.
那个知名人士实质上是个坏蛋。a councillor should have the collective interest of society at heart.
议员应当关心大众的利益。at heart，mr．lin does not approve your proposal.
林先生的心里并不赞同你的建议。mr．wang looks serious，but he is kind at heart.
王先生看来严肃，但实质上他很仁慈。
by heart: 意思是“背诵”、“熟记”（by rote；to learn so well that one can remember it perfectly）。i know this poem by heart.
我能背诵这首诗。i don't see the point of learning by heart all the dates in the history book!
我真不明白为什么要把历史书里所有的日期都要记下来！英语解释：
副词 at heart:
in reality同义词：at bottom, deep down, inside, in spite of appearance