If you want to build one, it's best if you take the earthgears.stl and split in your slicer to arrange it manually. Do the same if you want to have individual parts.
You need eight pinpegs (the small part in EarthgearsCenterPinpeg.stl) and one of the center part (the big one in the same file).
If you want to do one with the openscad file, place the heart.stl in the same folder where your Earthgears.scad is.
Be aware of a very long rendering time. It took several hours on my machine (which is not the fastest one ;-)) because the rendering detail is apparently ridiculous.