The Tynecastle Park club were keen to land the forward on loan from Everton following his successful stint during the second half of last season.
Hearts made a strong push for his return but manager Robbie Neilson was wary of the potential offers from English Championship clubs who would be able to contribute more towards the player's wages which were understood to be as much as £15,000.
"It was always one that was probably going to be outwith our means anyway," Neilson said after the arrival of Lawrence Shankland.
“We are pushing the club forward and the board have been outstanding backing us but there are levels we can’t get to. That’s probably one that we can’t.”
The 21-year-old, who scored seven goals in 20 games and became a fans’ favourite at Tynecastle Park, has since revealed a return to Hearts was not on the cards once a move to the English second tier was a possibility.
"It feels great to be here - it’s such a massive club,” he said, as per the Daily Record.
“As soon as Sunderland showed an interest, I knew this would be a great environment for me to continue my development and a great platform to show what I can do.
“I’ve played in League One and the SPL (sic), so this is the next step for me and I feel I’m ready for the Championship.”