If your casualty is NOT BREATHING, you must also assume that his heart has stopped. This is known as CARDIAC ARREST - 'Cardiac' means 'heart' and 'arrest' means 'stop'.
Once you have established that there is no heartbeat by confirming absence of normal breathing (and an ambulance has been called) continue with 30 CHEST COMPRESSIONS as follows and then TWO inflations (rescue breaths).
The main changes in these new guidelines are as follows:
1. No need to check inside the mouth unless history dictates. See also choking.
2. Position your first hand in the centre of his breastbone.
3. Start with 30 chest compressions, concentrating on 'quality', i.e. keeping up depth of 4-5 cm.
4. Share 'compression duties' every 2 minutes if possible before getting tired.
5. Take only one second (duration) to deliver each inflation (rescue breath).
6. If the chest doesn't rise make no more than two attempts before moving back to compressions.
NOTE: There is no circulation check now. Once you have decided that the casualty is not breathing, we are told to assume the heart has also stopped.