Motherwell ended Hearts' clean sheet record at Tynecastle with an equaliser in the fifth minute of stoppage time.
Substitute David Milinkovic opened the scoring for the hosts on 80 minutes, but Curtis Main appeared to get the final touch to the visitors' equaliser in the dying seconds. That brought an end to Hearts' club record eight-game run without conceding a goal, although they remain unbeaten in their last 12 matches.
They looked certain to hold on for victory after taking the lead with only ten minutes of regulation time left. Motherwell refused to give in and gratefully accepted a point when Main's header crossed the line following a penalty-box scramble.
Hearts hosted Foundation Day throughout the afternoon in recognition of more than £6.5million contributed by fans through Foundation of Hearts since 2014. Outside the new-look Tynecastle Park, the Foundation Plaza was officially opened to thank supporters for their pledges. Inside, much of the intrigue surrounded new signing Danny Amankwaa. He started as a substitute.
The hosts came close in the opening ten minutes when Ross Callachan and Tom Aldred challenged for a cross and the ball rebounded off the post. A physical contest was developing between two competitive teams who had to cope with a strong blustery wind. Anthony McDonald was back in the Hearts' starting line-up and could have scored on 22 minutes. He collected Callachan's pass and cleverly evaded Charles Dunne but shot waywardly over the crossbar.
That began of a run of opportunities for those maroon. Home players and supporters appealed loudly for a penalty when Callachan's header appeared to be blatantly handled by the Motherwell defender Cedric Kipre. Referee Willie Collum let play continue. Moments later, the visiting goalkeeper Trevor Carson made a double save as Steven Naismith and Callachan dispatched attempts from distance.
The Lanarkshire side thought they had broken Hearts' clean sheet record near the half-hour mark - only striker Main's backheeled flick was disallowed by an offside flag. Then came another vehement penalty appeal as Callachan fell inside the box when he was tackled by Aldred. Collum signalled that the centre-back played the ball first. Main's diving header from Nadir Ciftci's cross bounced agonisingly wide of target as openings continued to arrive for both teams near the interval.
Hearts saw goal attempts from McDonald and Demetri Mitchell go close after the break before Amankwaa made his debut by replacing McDonald. However, it was another substitute, Milinkovic, who broke the deadlock ten minutes from full-time. Michael Smith's free-kick wasn't cleared properly by the visiting defence and Milinkovic arrived to side-foot the ball beyond Carson with the aid of a slight deflection.
That looked to be enough to win the game but five minutes of added time allowed Motherwell the chance to force a leveller. Craig Tanner's free-kick was headed back across goal by Andrew Rose, Aldred's shot was deflected and Main headed goalwards as the ball squirmed over the line. Hearts players protested but the equaliser stood in a dramatic ending to the match.
Hearts (3-4-2-1): McLaughlin; Souttar, Hughes, Berra; M Smith, Djoum, Irving (Randall 84), Mitchell; McDonald (Amankwaa 70), Callachan (Milinkovic 64); Naismith.
Unused subs: Hamilton, Brandon, Cowie, Zanatta.
Motherwell (3-5-2): Carson; Kipre, Aldred, Dunne; Cadden, Campbell (Bigirimana 76), McHugh, Rose, Tait (Petravicius 84); Main, Ciftci (Tanner 55).
Unused subs: Griffiths, Grimshaw, Hartley, Turnbull.
Referee: Willie Collum.