The 05ers failed to beat their visitors in two contests last season, but FCH have just suffered two heavy defeats for the loss of seven goals.
Match preview
Finally posting their first league win of the season, Mainz managed to ride their luck away to Augsburg last week, taking maximum points despite facing some 29 shots: since such records began, only three teams have ever won a Bundesliga match after conceding so many attempts.
It was all the more remarkable, as they were reduced to 10 men during the first half, before their hosts also had a player dismissed later on, but Jonathan Burkardt ultimately helped the O5ers secure a cherished 3-2 victory.
Mainz have now lost only one of their last 13 Bundesliga fixtures - both winning and drawing half of the other dozen - which was their most recent home game, against Werder Bremen.
Despite leaking an overall total of 86 shots this season - a league high - Bo Henriksen's side have stayed competitive by posing a threat at the other end, scoring eight goals in their first four matches - the club's best tally at this stage since 2016.
Interestingly, half of those goals have been headers - including two last time out. That is also a league high, giving cause for Heidenheim's faltering back line to fear their trip north this weekend.
It may have taken until matchday 15 last season, but Heidenheim's first ever Bundesliga away win finally came along at Mewa Arena, and since that 1-0 success they have lost just two of their next 11 away fixtures.
However, their most recent road trip resulted in a 4-2 defeat to Borussia Dortmund, which was then followed by a serious setback on home turf last weekend.
Heidenheim's 3-0 loss to Freiburg was their first time they had suffered back-to-back defeats since March, and they have only lost three consecutive Bundesliga games once before - back in October of last year.
Frank Schmidt's side had hitherto been in fine form, but only Holstein Kiel have shipped more goals across the last two weeks than FCH, who have conceded more times than throughout their previous eight top-flight fixtures combined.
Nevertheless, they still sit one point above Mainz in the standings and just three shy of second spot, with their European league-phase debut scheduled for next Thursday.
Mainz 05 Bundesliga form:
Mainz 05 form (all competitions):
Heidenheim Bundesliga form:
Heidenheim form (all competitions):
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Team News
Bo Henriksen must make at least one change to a winning team, as Nadiem Amiri was sent off for the first time in 230 Bundesliga appearances last time out. He must now miss a Mainz game due to suspension for just the second time.
Nikolas Veratschnig and Bayern Munich loanee Armindo Sieb are both doubts because of injury, but the hosts should otherwise have a full squad available.
Since the start of April, only Bayer Leverkusen star Florian Wirtz has scored more Bundesliga goals than Mainz striker Burkardt (seven) among German players; however, the latter's last six have come all away from home.
Meanwhile, Heidenheim will only be without midfielder Julian Niehues due to a knee injury, so Frank Schmidt has a full hand to choose from if he decides to shake up an ailing side.
USA international Lennard Maloney should still start in the visitors' engine room, though, with Marvin Pieringer leading the line up front.
Mainz 05 possible starting lineup:
Zentner; Kohr, Jenz, Hanche-Olsen; Caci, Sano, Barkok, Mwene; Hong, Lee; Burkardt
Heidenheim possible starting lineup:
Muller; Traore, Gimber, Mainka, Fohrenbach; Maloney, Schoppner; Conteh, Wanner, Scienza; Pieringer
We say: Mainz 05 2-2 Heidenheim
Only Werder Bremen have taken fewer shots than either of these teams this season; however, only Bayern Munich have a better conversion rate than Heidenheim, and Mainz are not much further behind.