The expressions " Heart " part 1

1. By heart ;  

If you know something by heart, you’ve learned it so well you know it from memory


2.  To your heart content ;

If you do something to your heart’s content or desire, you do that thing until you are satisfied.

3.  Eat your heart out ;

Losing a race that you really, really wanted to win might cause you to eat your heart out, or wallow in grief.

4.  Have your mouth in your heart ;

It refers to a heightened state of anxiety or fear. There are many things that might bring your heart all the way up to your mouth,