Penguin the heading on that wikipedia page is more or less telling you that the information shouldn't be quoted. Is there only one citation for that whole passage?
Oy, anax, you really love to make us work. I'll get you your nice hot steamy bowl of cited passages.
This is what happens:
http://people.howstuffworks.com/lethal-injection2.htm And as for what leaves them dead:
The Process
•The prisoner is bound to a gurney; two needles are inserted into the prisoner's veins and a saline solution is injected.
•Sodium thiopental, an anesthetic, is injected to put the prisoner to sleep.
•Pavulon, or pancuronium bromide, is released, inducing paralysis and stopping breathing.
•Finally, the flow of potassium chloride stops the heart. This chemical can cause excruciating pain if the prisoner is still conscious.
Courtesy of:
http://www.amnestyusa.org/death-penalty/lethal-injection/page.do?id=1101012