According to the AHA, evidence now indicates that the survival of a cardiac arrest victim depends principally on effective chest compressions to provide adequate blood flow to vital organs until a normal cardiac rhythm can be re-established. Studies have shown that half of chest compressions given by professional rescuers are too shallow and that CPR is interrupted too often during resuscitation attempts. For this reason, new guidelines simplify lone-rescuer CPR, emphasizing the technique of "push hard and push fast" to improve the efficacy of chest compressions. The AHA advises that rescuers allow the chest to recoil completely after each compression and try to use equal compression and relaxation times. 

To improve the quality of administered CPR, new guidelines recommend that lone rescuers provide a compression-to-ventilation ratio of 30:2 for all victims 

. During two-rescuer CPR, a compression-to-ventilation ratio of 15:2 is used when resuscitating an infant or child, and a ratio 30:2 is used when resuscitating an adolescent or adult. (In the 2000 guidelines, adults were administered CPR at a 15:2 ratio; infants and children, at 5:1-during one- and two-rescuer CPR.)  And when an advanced airway is in place, two rescuers no longer pause chest compressions to deliver rescue breaths-again, the idea is to provide continuous effective chest compressions to maximize blood flow. 