“在心底”常见的英文表达有 “in one's heart” 或 “deep in one's heart”，以下为你详细介绍：
含义：强调内心深处的情感、想法或信念，是一种较为宽泛的表达，指在内心比较核心、重要的位置。
例句：
She knew in her heart that he was the right one for her.（她在心底里知道，他就是那个对的人。）
Even though he said he didn't care, I could tell he was hurt in his heart.（尽管他说他不在乎，但我看得出他心底里还是受伤了。）
含义：比“in one's heart”程度更深，更强调内心最深处、难以言表或隐藏很深的情感、想法等。
例句：
Deep in her heart, she always dreamed of becoming a famous writer.（在她内心最深处，她一直梦想着成为一名著名作家。）
Deep in his heart, he regretted not spending more time with his family.（在他内心深处，他后悔没有花更多时间陪伴家人。）