"Heart Shaker" is a song recorded by South Korean girl group Twice, the group's fourth Korean single of 2017. The song was released on December 11, 2017 by JYP Entertainment and distributed by Genie Music.

On November 27, 2017, JYP Entertainment announced the release of the Christmas-inspired reissue of Twice's first full-length album Twicetagram, titled Merry & Happy, on December 11. The title track "Heart Shaker" was revealed three days later. The song's title was previously teased on few scenes of the music video of "Likey". From December 4–11, several previews and teasers, including the song's lyrics, were released. The album, along with the music video for the lead single, was officially released on December 11. It was also released as a digital download on various music sites.

"Heart Shaker" is written by music production team called Galactika (별들의전쟁) and co-composed by David Amber, who also co-composed Hyoyeon's single "Mystery", and Sean Alexander, co-composer of the hit single "Lion Heart" by Girls' Generation.

Tamar Herman from Billboard described the song as a "bright pop song [that] incorporates funky guitar riffs, twinkling synths, and soft harmonizing to create a vintage wintertime feel, but with an upbeat melody and impish delivery of the verses and the energetic chorus". Lyrically, it captures the feelings of a girl as she courageously reach out for a confession to someone who has "shaken" her heart.

A minute-long music video teaser for "Heart Shaker" was released on December 4, 2017. It features Twice in white long-sleeved T-shirts and jeans performing the chorus of the song on a set that looks like a store. Along with the album release, full version of the heart-themed music video was uploaded online on December 11. Unlike their previous Korean singles, it is heavily dance-oriented in variety of vibrant and retro-inspired sets. It ended with doubling the members in a finale dance sequence that offers up an eighteen-member Twice through mirrored choreography.

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