To have learned or memorized something completely. Ask Becky to recite the poemshe knows it by heart.I can't sing that song in front of an audience if I don't know the words by heart!See also: by, heart, know
know something by heart
Fig. to know something perfectly; to have memorized something perfectly. I know my speech by heart.I went over and over it until I knew it by heart.See also: by, heart, knowSee also: