Heinen spent the past two seasons with the Penguins registering 141 total games. He scored 22 points in 65 games last season with Pittsburgh.
He will be returning to Boston, the team that originally drafted him. He played his first four seasons in the NHL with the Bruins and saw his best campaign come in 2017-18 where he scored 47 points.
He will now shift his focus towards earning a contract with the Bruins.