5ma will not stop your heart. 5ma is "safe", which is why GFCI is set to not allow any more than that.
Just like radiation levels, there is no actual current level that is garunteed to kill you- but at somewhere around 20-100ma through your heart, it will stop beating properly. In this range, muscle action is also inhibited, preventing the victim from escaping the shock.
FYI, there was a man once killed himself with a 9V battery during a classroom exercise. He pierced his skin with the ohmeter probes, lower the contact resistance to the point where he recieved a lethal shock through his heart. It does not take much!
"one hand rule", anyone?