[blueskin_]

Legal death is arbitrary as it's just a decision by a trained person. People have been revived after 10 minutes or so after 'drowning' in cold water. Even in cases of heart failure, pronouncement of death is when the doctor/nurse feels further efforts to revive would be futile. In the long past, someone who would today be revived in that case might have been pronounced dead earlier; the issue is that resuscitation efforts are stopped immediately after pronouncement of legal death - if they were not, it would be a more common occurrence.