A person performing CPR should begin by making sure paramedics are on their way and the victim is in a safe location. The person performing it should then center his hands on the victim's chest and perform compressions at a rate of approximately 100 beats per minute.
The first thing to do in any emergency is to call 911 for assistance. If there are two people available, one should call while the other begins CPR. If only one person is available, that person should call before beginning CPR.
If an AED machine is available, it may be appropriate to give the victim one shock before beginning chest compressions. Instructions for using the machine are located with it.
People trained in CPR may take additional steps such as making sure the victim's airway is clear and performing rescue breathing, but the Mayo Clinic recommends that untrained people focus on chest compressions. To perform them correctly, the person should place one hand in the center of the chest between the nipples, then place the other hand on top of it. He should then keep his elbows straight and center his shoulders over his hands, then press strongly on the chest using his palms rather than his fingers. Compressions should be performed rapidly and the chest should be allowed to rise completely before the next one is done. They need to be done firmly enough to push the chest down approximately 2 inches.