Eighteen-year-old Conor Pepper rescued a draw for the Highlanders after they had appeared dead and buried at the break - two goals down and a man down following a tempestuous first period.
Arvydas Novikovas had given the hosts the lead on 15 minutes, curling past Ryan Esson, before John Sutton doubled Hearts' lead after a debatable penalty award.
Richie Foran was shown a red card on the stroke of half-time, prompting the fury of Terry Butcher, but Caley were handed a lifeline with a penalty of their own, Andrew Shinnie netting. Pepper then sparked wild celebrations among the visitors deep into injury time.
Novikovas was drafted in to replace David Templeton, serving the first of a two-match back for kicking Hibs captain James McPake.
Danny Grainger returned to the starting eleven, with young Kevin McHattie dropping to the bench, while Mehdi Taouil was charged with infusing the hosts with creativity, coming in for Scott Robinson. New signing Peter Enckelman had to be content with a place on the bench.
Inverness, still unbeaten in the SPL after draws against St Mirren and Kilmarnock in their opening league fixtures, showed just one change from the previous week with the suspended Owain Tudor-Jones making way for Foran.
And it was the visitors who made the more impressive start to the encounter, threatening MacDonald's goal twice in the first 10 minutes.
First Andrew Shinnie fizzed a low drive just past the post before his brother Graeme produced a sensational ball into the box across the face of goal - but there were no willing takers for the inviting delivery.
However, it would be the home side who claimed the lead after 15 minutes. A fine counter-attack saw Andy Driver power into the Caley half before finding Darren Barr. His through-ball was perfectly weighted into the path of Novikovas in the right channel of the box, and the Lithuanian winger calmly slotted the ball past Ryan Esson.
The game endured something of a lull, lacking in goalmouth action, until controversy reigned on 42 minutes.
Referee Bobby Madden decided that Simon King had fouled Sutton as the striker attempted to get on the end of a Taouil free-kick and Sutton stepped up himself to lash home his second goal of the season from the spot.
Marius Zaliukas, who also clashed with Esson during the same hectic incident, limped off to be replaced by Scott Robinson.
Madden then further infuriated Inverness on the stroke of half-time, showing a red card to Foran - himself returning from suspension - for a reckless challenge on Ryan McGowan.
Caley manager Butcher was moved to angrily confront the official at the break - and the man in the middle was the centre of attention once more in the second period.
He awarded Butcher's side a penalty kick of their own approaching the hour mark, following a challenge by Paterson on Graeme Shinnie. It was sibling Andrew who did the business from the spot, firing his effort from 12 yards into the roof of the net, despite MacDonald getting a touch.
McGowan should have restored the Tynecastle side's two-goal cushion midway through the second half when he was sent scampering through on goal by a delightful chipped Robinson pass, but dragged his shot wide.
Jambos full-back Paterson was next to threaten, fizzing a shot just wide, but the hosts paid for an underwhelming second-half display with the last kick of the game.
Graeme Shinnie crept in behind the Hearts defence and lofted the ball past MacDonald, allowing Pepper to lash home.
