Doesn't recognise my class

[Barguast]

This is a little hard to explain, but here goes.
I have two classes which are defined in separate header files. For the sake of this message, I'm just call them 'Class1' and 'Class2'
These two classes use each other, so I tried to do this:

In Class1's header file

#include <Class2.h>

In Class2's header file

#include <Class1.h>

Both headers have '#pragma once' to avoid redefinition errors.

The problem is then when the Class1 symbol is used in the Class2 header, it is not recognised (and vice verse).

Maybe I've not explained this well enough, but I'll try to be more specific if you ask.