French midfielder Martin, 30, was signed on a three-and-a-half year deal in January 2017 by former head coach Ian Cathro. He made 21 appearances, scoring two goals. His last outing in a Hearts shirt came against Kilmarnock at Rugby Park in August 2017.
Current boss Craig Levein admitted to the Evening News in March this year that Martin wouldn’t feature in his plans, saying: “Basically, he’s the type of player Ian (Cathro) wanted his team to play with but he’s not the type of player I want my team to play with. He just doesn’t fit in with what I want to do.”
Striker Keena, 19, who joined Hearts in August 2017 from St Patrick’s Athletic and has made two first-team appearances, enjoyed a successful loan spell at Queen’s Park last season. He is currently recovering from a hernia operation and will head to East End Park once fit.