An excellent set of results since Nenad Bjelica took charge has quickly ended Union's fears of facing relegation after a woeful start to the season under Urs Fischer.
Match preview
That fine form continued last weekend as Union beat Hoffenheim by one goal to nil; Brendan Aaronson scoring the only goal of the game after both played the second half with 10 men.
Since Bjelica took charge in the capital, only four teams in the division have won more points than Union's tally of 17, moving them eight points clear of the relegation zone.
Such a healthy distance clear of the drop seemed a pipe dream just a few months ago, as Union had spent much of the campaign bottom of the league.
A pragmatic approach has paid off for Bjelica, as only three teams in the Bundesliga have scored fewer goals since his appointment, but that has not prevented them from picking up results.
Only runaway league leaders Bayer Leverkusen have conceded fewer across the last 10 games, as all of their wins so far in 2024 have been by a 1-0 scoreline.
Heidenheim were one of the many sides who beat Union during their barren run of results earlier in the campaign, and they have continued to improve.
Frank Schmidt's side saw their eight-game unbeaten run come to an end last weekend though, as they were beaten 2-1 by leaders Leverkusen in a performance that will have still delighted the manager.
After sitting 14th and well in the mix of relegation as recently as December, 15 points across their last nine games have moved Heidenheim a comfortable distance away from the drop in their debut Bundesliga season.
Instead, sights may well be set on chasing a European spot, but that will heavily depend on whether the DFB-Pokal winner will allow seventh place to qualify.
Heidenheim sit six points adrift of Eintracht Frankfurt in sixth, but they are just two points shy of seventh, with a large number of clubs, many of who have been inconsistent, battling for that final potential place.
Union Berlin Bundesliga form:
L
W
L
D
W
W
Heidenheim Bundesliga form:
D
D
D
D
W
L
Team News
Kevin Volland's late first-half dismissal at Hoffenheim means the Union striker will be suspended for this clash, with last week's match-winner Brendan Aaronson in contention to come in.
Bjelica has revealed Chris Bedia is struggling to adapt to German football, so there could be a tactical switch to accommodate for Volland's absence, with Yorbe Vertessen another player who could come in.
Diogo Leite is also suspended after being booked last weekend, and Bjelica was tight-lipped about whether he will go to a back four, or bring either Robin Knoche or Paul Jaeckel in to play as part of a back three.
Heidenheim will be able to call upon Denis Thomalla once again after recovering from illness, but a lack of match fitness and time on the training ground may see him settle for a place on the bench.
Apart from long-term injury absentees Thomas Keller and Elidon Qenaj, manager Schmidt has a full set of players to choose from for this trip to Berlin, and they could remain unchanged.
Union Berlin possible starting lineup:
Ronnow; Juranovic, Vogt, Doekhi, Gosens; Aaronson, Tousart, Khedira, Laidouni, Vertessen; Hollerbach
Heidenheim possible starting lineup:
Muller; Traore, Mainka, Gimber, Fohrenbach; Schoppner, Maloney, Beck; Dinkci, Kleindienst, Beste
We say: Union Berlin 1-1 Heidenheim
Heidenheim have a superb record against Union, with most of their meetings coming in the second-tier at the end of the 2010s, winning six of the previous nine - losing only once.