(verb) to have something memorized perfectly
Example Sentences:
The piano player had to learn the piece of music by heart so he could perform it.
A: Do you know all the words to The Star Spangled Banner?
B: Yes, I learnt it by heart.
The audience was surprised when the karaoke singer sang all of the songs without words, but he had learned all of the songs by heart.
From the Blogs:
Teaching Children to Learn by Heart
Media:
Similar idioms: