when do they play chasing cars in grey's anatomy
It was released on 6 June 2006.
Chasing Cars
 It was recorded in 2005 and released on 6 June 2006 in the United States and 24 July 2006 in the United Kingdom. 
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Chasing Cars [SEP] Introduction
"Chasing Cars" is a song by Scottish-Northern Irish alternative rock band Snow Patrol. It was released as the second single from their fourth studio album, "Eyes Open" (2006). It was recorded in 2005 and released on 6 June 2006 in the United States and 24 July 2006 in the United Kingdom. The song gained significant popularity in the US after being featured in the second season finale of the popular medical drama "Grey's Anatomy", which aired on 15 May 2006. "Chasing Cars" became notable as one of the songs that revealed the impact of legal downloads on single sales in the UK, selling consistently for years after its release.