Hi Mike, it's because of the way the hearts are constructed - they don't actually come to a sharp point at the top and bottom point spots, instead the curve is extremely tightly bent in those spots, basically bending back on to itself in a super tight 180 degree turn.

That essentially makes the side walls of the heart to be self intersecting surfaces, meaning the surface pushes through its own self. Usually self intersecting surfaces will cause problems in surface/surface intersection calculations.

You'll probably need to reconstruct the hearts to instead be made up of 2 segments that meet each other at a sharp top and bottom point rather than one long single curve that has such a super tight internal back-tracking bend in it. The easiest way might be to cut the heart curve in half by a dividing line with the Trim command, and then maybe use the Rebuild command on it (set up a shortcut key with Rebuild as the command name) to reconstruct it to get rid of any remnant of tightly bent areas...

Let me know if this is not clear.

- Michael