know something by heart 默记，背诵出，背熟

【例句】
He knew all his lines by heart two weeks before the performance.
在上台表演前的两个星期，他就把自己所有的台词记得滚瓜烂熟了。

You need to know this piece by heart next week.
你需要在下个星期将这个部分记得滚瓜烂熟。