6 pages.

You can simply have children cut on the bold line of their folded paper (they will be amazed to see they have created a whole heart when they unfold it) or you can have children cut the heart and "scrap" paper in half and glue them to another sheet of paper to make a positive-negative reverse piece of art. 

You can also turn this into an interesting writing prompt for older students.  I've included an example for clarification.  Completed projects make an awesome February bulletin board.