Boss Nigel Clough has made his fourth signing of the January transfer window.
United have secured the services of Hearts highly rated midfielder Jason Holt on-loan for the rest of the season, with the view to a permanent transfer in the summer.
The 21-year-old Scot, who has been capped by his country at U19, U20 and U21 level, made his Hearts debut as an 18-year-old against Dundee United in the SPL in May 2011.
Of Holt, boss Clough commented: "He is an exciting young midfielder and having him for the next three or four months gives us the opportunity to have a good look at what he offers.
"We are aware that we are well covered in the midfield area but we have a busy second half of the season coming up and we hope he can make an impression like when Stefan Scougall came down here a year ago."
Holt said: "I'm delighted to be given an opportunity at a club like Sheffield United. The season has gone tremendously well so far at Hearts and I'm proud to have played a part. I'm looking to playing more football, and hopefully I will be afforded that chance at Bramall Lane."
Hearts head coach Robbie Neilson has given the move his backing, adding: "It's a great chance for Jason to go to different surroundings and try to impress."
Having enjoyed a successful loan spell with Raith Rovers during the 2011/12 campaign, Holt gradually managed to establish himself in the first-team at Tynecastle over the following two seasons.
This term, the Musselburgh born operator has been a regular in the The Jambos team that currently has 13 point lead over Rangers at the top of the Scottish First Division, as Hearts target an instant return to the SPL.
Last week, the Blades announced the signings of Paul Coutts, Kieron Freeman and John Brayford.
(Photograph courtesy of SNS Pix)