A solid heart made from a obj that was free to download. Spent a lot of time removing the inside meshes and making it all watertight. It is still a difficult piece to 3d print and I haven't figured out a good angle for it. Let me know if you find a good one.
You can either print the whole model (heart.stl) or you can print the top and bottom and connect them with two connecting pins. I printed my connecting pins at 0.85 scale.