Used openSCAD to cut the heart from the dragon model.
OpenSCAD didn't want to work with the full resolution version of the dragon so I trimmed it down a bit in meshlab. (dragon_lowres_ascii.stl) I used the heart thing http://www.thingiverse.com/thing:6190 to clip the heart from the original model. Then clipped the bottom of the heart so it could be used as the heart for the final print.
I printed this in parts and it seems there isn't enough gap between them. They don't fit together very well. Probably due to slicing/printing errors. So you may find that scaling the heart down a tiny bit might help.
Also my print is scaled up 2.77 times which might make for more fitting problems. Getting the heart in there was tricky. I wound up having to heat the leg a bit, slip the heart in and bend the leg back. I used PLA, ABS may be more forgiving. The heartless-dragon.stl and dragons-heart.stl are the files for printing and they are the original poster's size.
Perhaps you dual-struders could do a nicer job. The models are located wrt each other and should be usable in that fashion.
The SCAD file, dragon_lowres_ascii.stl and heart.stl are included in case anyone wants to do a bit better with the SCAD-ing. NOTE: I had to go in and trim a few polys I couldn't clip in openSCAD without sacrificing too much tail detail. Making the heart bigger to clip these polys wound up eating too much into the tail.
Great model, Thanks to Andreas for great Thing. If you print this version of the dragon please use the original thing (http://www.thingiverse.com/thing:17204) to display your "I made one"