Sorry the TARDIS is so fascinating aswell as all Time Lord Science, but one thing I just always think about is the TARDIS, I still remember being in awe learning that it has feelings in Series 1, I thought it was just a metal hollow shell. Basically do we know everything it can do, and why does a TARDIS have a heart? In Series 1 as someone said it turned Margaret Blaine into an egg and gave Rose the power of Gods. Has this been abandoned or will we ever learn more about it? Is it even still there in the console or is it in the engine room? Why didn't the Time-Lords use it in The Last Great Time War?

It's difficult to say because, as usual with Doctor Who lore, it changes throughout its appearances. In Terminus it was just a CPU-like thing the Black Guardian forced Turlough to tamper with, which ended up taking the TARDIS to the titular space station Terminus. Oddly enough that did turn out to be the exact centre of the universe and the start of the Big Bang, however.

'Why does the TARDIS have a heart?'

This is a figure of speech, with the 'heart' meaning 'the center'.

It was always said to be powered by 'the Eye of Harmony'. In Journey to the Center of the TARDIS the Eye of Harmony was shown to be a sun, frozen on the verge of collapse into a black hole.

What it is the power source for exactly is something of a mystery.