"Iron" is a song by Nicky Romero and Calvin Harris.

It became the second single to be released through Romero's label Protocol Recordings (after "WTF!?"

[1] A shortened version of the song was later included on Harris' third studio album, 18 Months (2012).

The majority of the song has an upbeat electro house style until vocals from Harris come in.

When the vocals do come in, the background tune is just a piano being played until Calvin Harris sings "Our hearts will never be the same again".