Thank you for the reply! The problem is that I essentially need a model of the /inside/ of the heart, and nothing else. And the space /between/ the heart and the box, and nothing else. And since the heart is hallow, subtracting it from the box also has the interior of the heart still left behind? I apologize if I am not making much sense, it is kind of abstract to explain. But I essentially have the heart in a box, but I need the two zero spaces as separate models. The inside of the heart. And the space between the outside of the heart and the box.

I keep going through different boolean process trying to figure out some combination that will allow me to do this, but one process seems to undo another and I am really kind of lost. Is there a way to "fill in" the heart model?