Heart of the TARDIS

The Heart of the TARDIS is the ship's soul. The connection to the Eye of Harmony is unclear. It has its location beneath the cental console, as configured by the Ninth Doctor. On one occasion it opened as if by itself ("Boom Town) and on another, it seemed 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. (The Parting of the Ways).

The presence of the Doctor in the first case, but not in the second, may example this inconsistency.

When Blon Slitheen looked into the Heart she regressed back to a Raxacoricofallapatorian egg (Boom Town).

When Rose Tyler did so she could telepathically operate the TARDIS, sending it to the TARDIS, taking it to Satellite Five. She also assumed god-like powers 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.