The Irishman is out of favour at Tynecastle and has been allowed to return to Rugby Park.
He scored 18 goals in 27 appearances for Kilmarnock during the first half of the 2010/11 campaign before joining Wigan Athletic. A £1.2m move to Derby County followed but Sammon failed to impose himself there and was loaned out three times before joining Hearts on a three-year contract last summer.
However, he has managed just one goal in 22 domestic appearances for the Edinburgh club and will hope to revitalise his career back at Kilmarnock.
Meanwhile, Hearts attacker Dario Zanatta has moved to Queen’s Park on loan until the end of the season.
The young Canadian enjoyed a loan spell earlier in the season at the League Two outfit, where he made ten appearances and scored one goal.
Forward Robbie Buchanan has joined Cowdenbeath on loan until the end of the season.
The 20-year-old moves to the League Two side, where he previously had two loan spells.
Under-20s player Yves Vladislav has left Hearts by mutual consent.