There is increasing evidence that mouth-to-mouth rescue breathing may not be necessary during brief periods of bystander cardiopulmonary resuscitation (CPR) for ventricular fibrillation. In contrast to ventricular fibrillation cardiac arrests, it has been assumed that rescue breathing is essential for treatment of asphyxial cardiac arrests because the cardiac arrests result from inadequate ventilation. This review explores the role of mouth-to-mouth rescue breathing during bystander CPR for asphyxial cardiac arrests. Clinical data suggest that survival from apparent asphyxial cardiac arrest can occur after CPR consisting of chest compressions alone, without rescue breathing. Two randomized, controlled swine investigations using models of bystander CPR for asphyxial cardiac arrest establish the following: a) that prompt initiation of bystander CPR is a crucially important intervention; and b) that chest compressions plus mouth-to-mouth rescue breathing is markedly superior to either technique alone. One of these studies further demonstrates that early in the asphyxial pulseless arrest process doing something (mouth-to-mouth rescue breathing or chest compressions) is better than doing nothing.