I 3D printed a couple heart shapes for Valentines day. For the first set I ended up using some EL Wire from Adafruit. I bought a few but only used the red one for this project:
Building on the lessons learned from the first design, I modeled the second design hollow. This heart also has a deeper channel around the edge to be able to fit a larger LED strip. This fit a flexible RGB strip also from Adafruit: