Heart of the TARDIS

The Heart of the TARDIS is the ship's soul. The connection to the Eye of Harmony is unclear.

When Blon Slitheen looked into the Heart she was reverted to a Raxacoricofallapatorian egg (Boom Town). When Rose Tyler did so she could telepathically operate the TARDIS and flew it to the Game Station (The Parting of the Ways). However, this power would kill her, so the Doctor sacrificed himself and took it himself.

It seems to take a great amount of strength to pull open the TARDIS console, revealing the Heart, such as a rift in space and time, or a large truck.