I used the very simple method (remember elementary school crafts) of folding a square in half and cutting a heart shape out of pieces of red felt. The larger the square, the larger the heart.
To make this a hanging decoration, I used twine. I looped a piece onto the back of the top piece and hot glued it down, adding a strip of burlap to keep it secure. I measured the space between each board and glued more twine down the back of each piece. Then trimmed off the excess twine.
When hanging it, I added another smaller felt heart to the point of the loop.