Hearts had a penalty claim rejected when Darren Randolph caught Callum Paterson with his knee as he collected a high ball but referee Crawford Allan ignored the appeals.
The game started well enough with Randolph diving well to push away Ryan Stevenson's powerful free-kick.
The controversy came in the 13th minute when Randolph and Paterson chased a high ball from opposite directions. The home player was favourite to get to the ball and did so but sparked an angry reaction from several visiting players after colliding with the Hearts striker.
On initial viewing, the Republic of Ireland international's trailing boot appeared to have come down on to Paterson's face but television replays showed the movement was entirely natural after Randolph caught the striker with his knee as he leapt for the ball.
Allan was ideally placed and re-started the game following treatment by dropping the ball to Randolph after deciding there was no intent or dangerous play.
Motherwell had stepped up a gear after the break but their crossing was consistently letting down their build-up play.
Randolph then saved from Jamie Walker but Hearts were becoming more reliant on the counter-attack.
Motherwell hit the bar midway through the half, but only as a result of another wayward cross as Humphrey's centre bounced on top of the goal frame.
Humphrey threatened again with 10 minutes left in more impressive fashion, beating Ryan McGowan on the edge of the box and firing a powerful effort that MacDonald blocked.
Henrik Ojamaa set up Higdon from the resulting corner but the striker could not get hold of his shot, and soon diverted the ball just wide of the near post after a cross from the Estonian, although he was challenged well by Marius Zaliukas.
Hearts almost snatched victory in the final seconds when Ryan McGowan headed just wide from a corner.