The recipe is quite easy to follow: head to Shapeways, order for printing two hearts (puzzle), deliver them to your Valentine :-)
It will be his/her task to put the pieces together (there are no hints in the box and having 2 models scrambled increases somewhat the difficulty)
Yes, Shapeways will "print" (3D) in different materials your 3D drawings or you can borrow from the existing designs published by their users and have the 3D model delivered to you.
PS. Sorry for breaking the news quite late to you, our "hearts" were ready just last night :-)