You get the Pale Hearts quest from San in the Shop of Occult (Inner City, close to the Old Catherdral). San asks you to collect Pale Hearts that you can obtain after killing stone statues. There are eight statues altogether, here are the locations:
- You encounter this as you find a dead body on the roof while approaching Tusker's hideout (part of the main story)
- Once you return from Africa two stone beasts will attack
- In the garden of the Eastern Villa
- In the Arsenal, exit the Doctor's house and go left a few hundred meters
- In the Outer City, in the garden before the Shadow Mask guild
- It is on the bridge where you obtain the Dark Views achievement
- In the West Wing of the Doge Palace