How will the Arc Reactor work?

Why does Tony Stark go into cardiac arrest when his arc reactor is removed?

• In Iron Man, Tony Stark gets shrapnel embedded in his heart after a bomb detonates near him. While held captive, his translator gives him an electromagnet powered by a car battery to keep the shrapnel from moving any further into his heart, a process that would take about a week to kill if not for the electromagnet. When he returns to the states however, he goes into cardiac arrest when Potts removes the copper coil from his chest, and later when Obadiah removes his arc reactor all together, you hear his hear beating, implying that he is NOT in cardiac arrest, and yet he is clearly in a state of serious medical distress. Why is it that Tony experiences such adverse medical problems when his reactor is removed, if all that it is supposed to do is prevent shrapnel from reaching his heart, a process that would take a week to kill him anyway? If anyone could clear this up I'd appreciate it, thanks!

• Answer:

  He says he's GOING into cardiac arrest, that means it is going to happen soon. He also could have just been saying that to simplify his condition to Pepper.