To feel in (one’s) heart of hearts – in a person’s deepest feelings. I feel in my heart of hearts that I shouldn’t marry that man. (I feel strongly that I shouldn’t marry him.)
Take it to heart – worry about, feel it is serious (usually feel bad about it). When Nancy’s boss said she wasn’t a good employee, Nancy took it to heart. (She felt very bad and serious.)
From the bottom of (one’s) heart – to really mean what a person says. You are so wonderful. I mean it from the bottom of my heart. (I really, really think you are wonderful.)
Heartfelt – (adjective) warm feelings, sincere. My grandma gave me a heartfelt welcome when I arrived. (Grandma was really happy to see me. I could see she felt good.)
With all (one’s) heart – completely, a person really means what he is saying (or doing). I love you with all my heart. (I really love you very much.)
To get to the heart of (something) – to find out the real reason for something, get to the center or find out what really happened. Who caused this problem? We need to get to the heart of it immediately. (We need to find out what happened.)
To feel a hole in (one’s) heart – a feeling of sadness (usually because someone is gone.) When James died, Susan felt like she had a hole in her heart. (Susan was very sad.)
To have a heart of gold – to be very kind. She was a wonderful and kind person. She had a heart of gold.
To have a heart of stone – to be very unkind, to not care about people or things. He didn’t care about anybody. He had a heart of stone.
Heart to heart – have a private conversation and say anything. I had a heart to heart talk with my daughter about dating. (Only the two of us talked. And we talked freely.)