The 22-year-old will be included in the squad for the Betfred Cup tie at St Johnstone on Wednesday, subject to international clearance.
He arrives from Polish top-tier side Pdobeskidzie Bielsko-Biala under freedom of contract.
"I feel Krystian will be a quality addition to the squad," head coach Robbie Neilson told the club website.
Hearts have confirmed the signing of Polish defender Krystian Nowak on a two-year deal.