Kevin McHattie has signed a three-year deal with Kilmarnock on the same day that he left Hearts by mutual consent.
The 22-year-old left-back made more than 80 first-team appearances for the Jambos, many of those under Gary Locke, now manager at Kilmarnock.
"I am delighted to have signed for Killie and I can't wait to get playing first-team football," he said.
"I have worked with the manager before and after I spoke to Dale (Carrick) I was certain this was the right move."
Locke told the Killie website: "I am pleased to have secured Kevin for Kilmarnock. He is a very talented young left-back and we had to fight off competition from some really big clubs to sign him."
Earlier, McHattie told the Hearts website that he was leaving "with some great memories, not least winning the title last year. I'll miss this place".
Meanwhile, Kilmarnock's 18-year-old goalkeeper Devlin MacKay has joined Derby County on loan until January 2016.