This is an anatomically correct human heart. It is created as a multi material version: The heart's Ateries, Atrium, Valve, Ventricle, Papillary and Veins are a seperate file, so you can print a fancy multicolor heart ;-) The Ventricle has some holes which makes it possible to see the Valves and Papillaries inside the heart.
It is a rather complex model, but looks aweseome once it is finished!
You only need support for the bottom of the heart if you use the orientation from the stl files (see the last picture). The inside of the heart will then print okay without supports.