For you Illusionist locket fans, the Mechanical Philosopher has another possible design that is very well thought out and presented. I've been corresponding with some people who are struggling to actually build this thing, rather than just come up with a spiffy design like me and MP. So out of sheer guilt, here's a simpler (and buildable) design. I'm only including one side, but the other side is nearly identical.
The only major disadvantage of this take is that halfway between heart and capsule formation you would be able to turn the lid until it came all the way off. It wouldn't fall apart easily because of the grooves, but if you played with it you could pull it apart.