I’ve done a few “surprise” cakes, though not one like this – which is awesome. But since no one else has responded… It looks like there are two layers made the same way, with one inverted over the other. First go read the tutorial here: http://iambaker.net/heart-cake-tutorial/. She shows how to carve the layers and fill them.
It seems like you can bake the purple layers (looks purple on my screen), then carve out a V-shape, line it with yellow cake strips, then fill with green cake-pop filling. I suppose you could also carve a green cake, but that seems more difficult to me. Good luck!