Hearts returned to the top of the Scottish Premiership but dropped what could be crucial points in the title race at bottom side Livingston.
The Jambos were playing catch-up following and were stunned by an early opener when Livingston opened the scoring after just five minutes.
Lawrence Shankland made his first start since January and headed in the equaliser before half-time in wild weather conditions that switched between snow and sunshine.
Hearts thought they had wrapped up the win against the relegation favourites when Claudio Braga headed into the net, but Lewis Smith slammed in for 2-2.
Marc Leonard hauled down Robbie Muirhead in stoppage time and the Hearts midfielder was red-carded following a VAR check.
Derek McInnes' side are one point clear of Rangers at the top of the Scottish Premiership with six games left to play. Livingston are 11 points adrift at the bottom.
Although they ended the weekend a point clear at the top, there was a huge sense of frustration among the 7,000 travelling supporters at Almondvale after the Edinburgh side dropped points for the fourth away game in succession.
The Jambos were stunned after five minutes as Livi - without a win since August - went ahead from their first foray upfield.
Babacar Fati drove up the left and his cross was headed out by Jamie McCart as far as Scott Arfield, whose shot was blocked by McCart.
The ball ricocheted back to May, who drove a precise low shot into Alexander Schwolow's bottom right-hand corner from the edge of the box.
Craig Halkett then had to stand firm to stop Mo Sylla forcing in a second for the Lions.
After this chastening start, Hearts started to get themselves into the ascendancy. Braga saw a shot on the turn saved by Jerome Prior before Alexandros Kyziridis was tantalisingly close to turning in Oisin McEntee's inviting delivery from the right.
Kingsley then blazed an angled effort just wide after overlapping Kyziridis on the left.
The equaliser came in the 24th minute when Cristian Montano failed to clear his lines and Leonard arrowed in a brilliant cross from the right that was powered home by the head of Shankland from six yards out.
Hearts' tails were up and Shankland almost struck again four minutes later when he blasted just wide after Braga headed a Kyziridis cross down to him on the edge of the box. Braga then saw a low shot from 18 yards tipped behind by Prior.
Hearts had three chances in quick succession just before the break, but Shankland twice and Kyziridis were unable to force the ball into the net after excellent work by Braga.
The Jambos got themselves ahead in the 51st minute when Kyziridis' cross from the left was headed back across goal by Shankland and Braga nodded in from a couple of yards out.
The visitors appeared to have control of proceedings as they went in search of a third, with Islam Chesnokov denied by Prior before Shankland headed wide at the back post.
But Livi levelled in the 58th minute when Smith forced the ball in from a tight angle at the back post after Joel Nouble had helped on a low cross from Montano, who had intercepted Halkett's pass to Chesnokov near the halfway line and surged up the left channel.
Hearts' frustration was compounded in stoppage time when Leonard was sent off for being deemed to have denied Muirhead a goalscoring opportunity.
Hearts head coach Derek McInnes speaking to Your Site:
"We've chucked away two points to be honest.
"The two goals we lost were awful and that has to be said because the first goal with the press is all wrong, people in between and we never really recovered that. But what we did do have was a good response.
"We had some good spells in the first half, great header and a great goal from Lawrence and it was more positive towards the end of the first half than anything.
"We spoke at half-time about just trying to move the ball a bit quicker. Livingston set up in a counter-attacking shape and on transitions they're always going to be a wee bit of a threat.
"It was more important that we really looked after the ball and at the start of the second half there were some good moments culminating in the second goal.
"You just felt the pressure was coming. We were so clean and polished and looked a team at the top end of the table. Instead of enjoying being in charge of the game and being in the lead, we inexplicably gifted Livingston a goal.
"You've got to credit [them], they work it and they find the extra man but it was so unnecessary and you keep coming off the canvas and going again with that. After that we huffed and puffed a wee bit and Livingston were good value for their point.
"Obviously, you look at the context there, we go top of the league with six games to go so we're not too negative or whatever but we've lost two points today from losing two very poor goals."
Former Hearts manager John Robertson on Your Site:
"Hearts go top, that's the big thing - psychologically that's good for them.
"But at 2-1 they were comfortable. It's schoolboy stuff, you don't play a straight pass into a midfield man. He gets caught and they spring, and from one of the worst misses of the season Livingston get a goal.
"After that, Hearts didn't do enough to win the game. I didn't think they asked enough questions of the Livingston goalkeeper or defence in the last half hour.
"In the end, it's a fair result. Between the two Livingston goals, Hearts could have put the game to bed but they didn't."
