Second division leaders Darmstadt 98 edged past Magdeburg 1-0 on Friday to secure their return to the Bundesliga after six years with a match to spare.
Darmstadt top scorer Phillip Tietz slotted in the 36th-minute winner following a VAR review to lift his team to 67 points, with one game left to play.
Heidenheim, in second place on 61, face Sandhausen on Saturday, while third-placed Hamburg SV are on 60 with two games left to play.
The top two teams win automatic promotion while the third team goes into a playoff with the 16th-placed Bundesliga team.