Forgive me if I sound really ignorant, as I have no medical training at all. A friend of mine "arrested" (I think), and although it is believed that he died instantly, when a visiting friend called for the ambulance she was instructed to perform CPR. When the ambulance crew arrived they also continued to try to resusitate him for about 15 minutes, and said that they always have to do so. I also live in the UK.