If somebody's heart stops while out in the street, lay rescuers should now focus on CAB (Compressions-Airway-Breathing) and not ABC (Airway-Breathing-Compressions) anymore, says the American Heart Association in its new guidelines. When a person's heart stops there is still some oxygen in their blood, but the circulation has stopped. Chest compressions help move blood around again straight away, while focusing on airways and breathing does not - the old system causes a delay... 
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