Most of the song is a slightly altered arrangement of the beat and bassline from the song "Breathe". The beat and bassline were very much part of Pink Floyd's playing style as far back as Atom Heart Mother. However, due to the altered beat and bassline, it is not directly related to "Breathe", unlike the last part of "Time" (sometimes listed in songbooks as "Breathe (Reprise)"), and "Any Colour You Like" (sometimes nicknamed "Breathe (2nd Reprise)").
When the Dark Side of the Moon suite was performed in 1972 (before the album was released), the song was completely different and went under the title "The Mortality Sequence". Then, it was simply an organ and samples of people speaking about death being played during the performance. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.