[1] The track, originally titled "Heartburn", has been described by the band's singer Gruff Rhys as a country and western song with lyrics that offer "soul advice".

[4][5] The music video for the song was directed by Jake & Jim and shows Super Furry Animals waiting to leave the planet Mars, having played a concert there.

[6][7] "Fire in My Heart" was originally called "Heartburn", a name which the group's singer Gruff Rhys felt was more poignant and gave the song "a twist", but other members of the band were not happy with the title so the name was changed.

[3] The track was recorded in the middle of 1998 at Real World Studios, Box, Wiltshire, along with the rest of Guerrilla, and was produced by the Super Furry Animals.

[8][9] B-side "The Matter of Time" was considered for inclusion on Guerrilla, but the band felt the album would be too self-indulgent if the song were added to the record's track listing.

During the bridge Rhys sings the lines "Oh the monkey puzzle tree has some questions for the watchdogs of the profane, and I ask, is it sad that I'm driving myself mad as this fire in my heart turns blue".

[11] A key change to F♯ major follows for the final verse, with Rhys repeating the line "I've got a fire in my heart for you" backed by multiple harmony vocals.

[6] The Melody Maker called the track a "lovely song, a real scarf-waver", although the magazine expressed disappointment that "Fire in My Heart" did not see the band "howling at the moon in their more deep-throated manner".

Ieuan and keyboardist Cian Ciaran are also shown looking at the Earth before the camera moves behind them to reveal hundreds of aliens stood in front of several minaret-like towers, waving at the group.