Luckily for the assassins, rather than order his driver to speed off, Heydrich told him to stop so he could go after the attackers.
Heydrich's popularity in the Czech Republic increased sharply, so
in Prague he felt very comfortable, even moving around the city in an open car without security.
As such, when the exposed car reached the bend in the road, one of the
would-be assassins, Jozef Gabčík, pointed his Sten Mark II at Heydrich at near point-blank range.
In a move that later resulted in Hitler calling Heydrich an idiot, Heydrich chose to drive his daily
commute in an open-top Mercedes, rather than in an armored car with extra guards, as you would expect one of the biggest mass murderers traveling in, essentially, enemy territory to do.