People can survive cardiac arrest if they receive only chest compressions during attempts to revive them — as advised by the current American Heart Association guidelines. But they cannot survive without access to oxygen sometime during the resuscitation effort, research suggests. Scientists tested different scenarios in an animal study of cardiac arrest. Rats received either 100 percent oxygen, 21 percent oxygen — the equivalent of room air — or no oxygen (100 percent nitrogen) at the same time they received cardiopulmonary resuscitation (CPR).