I love sitting in the shadows hearing about all the secrets these people have. It's amazing how much it fleshes out otherwise random thugs and civilians, especially when she says stuff like "If he doesn't die today, he'll take two more lives and then his own." Makes me wish I wasn't going non-lethal.
I spent a long time hearing all of her quotes when I first got the heart, and I got the impression that it was a certain person from how the voice sounded and the things it would say. Whenever it would describe its life, the dialogue is too oddly specific for it to not be someone we already know. I thought it might just be me, but the things that have been mentioned and how the heart stumbles whenever commenting on certain people and events makes it pretty clear to me.
There was also what Granny Rags says, if you visit her in the return trip to the Distillery District. She tells you a story about the Empress, mentioning something like her soul has survived and is bound and used for a purpose she doesn't know about.
"That's how Dad did it, that's how America does it, and it's worked out pretty well so far."
Corvo loved the Empress. The Empress was murdered and now Corvo wants to clear his name and get revenge for the Empress death. Corvo's heart was ripped out by the true assassin. The Outsider gives it back.....hmmm. I also thought about the connection. I think her spirit is bound to the heart that Corvo holds in his hand. Brain......farting.......