Tuchel, who took charge of the club in 2009, has led the club to seventh in the Bundesliga and within touching distance of a place in Europe next season.
"We're very happy with him and if he wants to extend his contract, then it would only take a matter of minutes," Heidel told Sport Bild magazine.
Tuchel has already led the club into Europe, by virtue of their best ever final league position of fifth in 2011, and with 33 points from the first 21 games of the current season they can challenge for another European campaign.
Seventh place would be enough for a berth in the Europa League should the two clubs contesting the final of the DFB-Pokal already have qualified for the competition via their league position, but Heidel insists his side cannot yet consider themselves among the Bundesliga's elite.
The signing of Koo Ja-cheol from Wolfsburg "will remain an exception", according to Heidel, whose side spent a club-record fee of 5million euros for the South Korean.