Study "Assembly.skp".

Print and assemble all pieces as shown in "Assembly.skp". I found "Heart.stl" prints best when the build plate is a little further from the print head than I normally set it. After printing, carefully remove the hold down pads on "Base.stl" and "Frame.stl".

Test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding will be required. Pay close and careful attention to the small gaps between the pieces of "Heart.stl", making sure to remove any flashing and/or debris with a hobby knife or equivalent as "Heart.stl" must move smoothly without binding.

Assemble as shown in "Assembly.skp".

Lubricate all contacting moving surfaces with light machine oil.

After final assembly and test, I apply a small dot of thick cyanoacrylate glue to heart lobes and point to hold "Heart.stl" securely if "Frame.stl".

Comment if you have questions.

Happy Valentines Day (also my birthday)!