"Flatline" is a song by English girl group Mutya Keisha Siobhan, which consists of the original line-up of the group Sugababes. Written by the trio alongside British artist Dev Hynes, who also produced it, it was released via digital retailers on 6 September 2013 by Polydor Records, who signed the band in 2012. It is a pop and R&B song in which the drums and the male backing vocals get gradually stronger until a climactic part. Lyrically, it addresses the deterioration of a relationship.