Question

If I learned sth by heart (and I know this is correct form), can I say: ' I know that by heart ' ? or not 'cause that's incorrect ?

Answer 1

You can say that.

 

Know / learn sth by heart are both correct.

Answer 2

I know that by heart. - jest poprawne i oznacza, że znasz coś na pamięć.

 

* After a few days of phoning Stephanie, he knew her number by heart.

  Po kilku dniach dzwonienia do Stefani, znał jej numer na pamięć.

* Actors have to learn their lines by heart.

  Aktorzy musze uczyć się swoich kwestii na pamięć.