Lead singer David Bayley stated that "Heat Waves" "is about loss and longing, and ultimately realising you are unable to save something". He said that "Also, this song is about memories and it's very nostalgic, and sometimes people feel more of that in the winter. Maybe that's part of the reason this song's hung around for so bloody long – everyone's
locked inside and trapped in their own thoughts." "Heat Waves" starts on a high and then drops into despair before rising again for a cheerful, optimistic finale, much like the crests and troughs of a real wave. Bayley came up with the chords one day while playing around on the guitar. He wrote the lyrics in just an hour, prompted by the death of a close friend whose birthday was in June. Bayley also described the song’s production process in the same Song Exploder episode. He explained that the opening guitar riff originated as a phone recording before being developed into the track’s central motif. The arrangement was built by layering elements, including a pitched-down vocal sample used as the bass line. Bayley constructed the vocal harmonies from numerous takes, adding ad-libs to create what he called a “choir of myself.” He emphasized leaving space in the mix by stripping back certain sections so that the lead vocal and beat would stand out.
NMEs Hannah Mylrea categorized the song as "earnest R&B run through the Glass Animals filter", and
Pitchforks Ian Cohen argued its guitars "could be plucked from any number of 'wavy hip-hop' sample packs meant to emulate
Frank Ocean's 'Ivy' on a bedroom producer's budget". A major theme on
Dreamland is the pursuit of brief pleasures to cope with the hardships of life, such as lust for others. On "Heat Waves", Bayley sings repeatedly, "Sometimes all I think about is you/Late nights in the middle of June." Another remix is a collaboration with American rapper
Iann Dior. A piano Simlish version was recorded by Bayley for
The Sims 4, and was featured in a limited-time "Sims Sessions" in-game music event in 2021. Sheet music for this song shows the key of
B major (in the C-sharp Dorian mode). ==Critical reception==