The 23-year-old follows in the footsteps of Demetri Mitchell, who spent 18 months on loan at Tynecastle from the Old Trafford club.
Pereira made two appearances for United in the 2016/17 season and another the following campaign. He's also spent time on loan at Rochdale, two stints in Portugal with Vitória de Setúbal and Belenenses, and finally a five-month deal with Belgian side Kortrijk in the second half of last term.
The keeper will provide competition for places with Hearts' first-team stoppers Zdenek Zlamal and Colin Doyle.
Doyle recently signed an extension to his contract, while Zlamal's deal is set to expire at the conclusion of this campaign.