[3] DeCaro had recently produced the albums Born Free, Love, Andy, and Honey for Williams, who recorded "Happy Heart" on March 8 of that year.

[4] Williams also performed the song for Clark's NBC television special Portrait of Petula that would air on April 7.

[5] A full-page advertisement in the March 22 issue of Billboard with the headline The Latest Thing from Paris showed a pair of bare legs standing in cleated running shoes and described the rush that Clark and her record company were in to get a recording of the song out: Last Monday.

"[7] Clark's recording appeared on her Portrait of Petula album, and in reviewing the LP for Allmusic, Joe Viglione wrote, "She does take the tempo of Andy Williams's 'Happy Heart' down a bit.

[2] Both recordings made their first appearance on the magazine's Hot 100 in the April 12 issue, which began a five-week run for Clark that took the song as high as number 62.

[16] Director Danny Boyle chose the Williams version for the soundtrack of his 1994 British film Shallow Grave, and in 2013 Rolling Stone revisited the scene in which it was used.

"As the twisty noir ends, Ewan McGregor, knife stuck through his chest, grins sublimely as his blood drips down onto the stacks of money stashed between the floorboards.

1BR is a horror movie about a young aspiring costume designer that moves into an LA apartment community which on the surface appears idyllic, unaware that they assimilate new tenants using operant conditioning" torture.

The female impersonator Holly Woodlawn lip-synced to the Clark version in the 1998 Tommy O'Haver film Billy's Hollywood Screen Kiss.

In the August 8, 1998, issue of Billboard, Dance Trax columnist Larry Flick wrote, "Speaking of revamping oldies, Junior Vasquez has done a fine job of tweaking Petula Clark's 'Happy Heart' into a thumpy house anthem" and added that "the track benefits tremendously from a rare peek into Vasquez's festive sense of humor.

He seems to be having a blast playing with Clark's girlish vocal, wrapping it in vibrant synths and wriggling percussion fills.