CPR is an emergency procedure done to help save someone's life who is not breathing or has no pulse. It involves chest compressions and rescue breaths. Chest compressions are used to artificially circulate the blood to the vital organs, while rescue breaths provide oxygen to the lungs. Because rescue breaths require a clear airway, they can be difficult to perform in certain situations. In addition, rescue breaths are not always necessary, as chest compressions alone can be enough to restart a heart in some cases. Therefore, if rescue breaths cannot be done safely or are not necessary, they should not be attempted.