The Polish defender was told he could leave Tynecastle this month if he found a new club. He heads to Greece hoping for a fresh start after falling out of favour under Hearts manager Craig Levein.
Nowak signed a two-year contract with the Edinburgh club in 2016 but could not establish himself as a first-team regular despite being able to play centre-back and centre midfield.
He made only one appearance after Levein replaced Ian Cathro as Hearts manager at the end of August.
Hearts Under-20 players Kyle Smith and Aaron Reid have also left the club by mutual consent.