External chest compressions provide artificial circulation. When you apply rhythmic pressure on the lower half of the infant's breastbone, you force the heart to pump blood.
To do external chest compression properly, follow the steps below:

2.  Make sure not to press at the very end of the breastbone.

3.  Keep your other hand on the infant's forehead, keeping the head tilted back.

4. Press down on the infant's chest so that it compresses about 1/3 to 1/2 the depth of the chest (Difference 5).

5.  Give 30 chest compressions. Each time, let the chest rise completely, with two mouth to mouth breaths in between each rep 1 second per each breath.

Relaxation and compression should take equal amounts of time. If you must give both rescue breathing and external chest compressions, the proper rate is 30 chest compressions to 2 breaths. You must compress at a rate of 100 times per minute. Keep interruptions to less than few seconds. Continue administration until help arrives.

Important:  As of October of 2008, AHA has revised its guidelines for performing effective CPR. If the person is not confident in his/her abilities of performing CPR, you should at minimum perform external compressions without mouth-to-mouth breathing, call 911 if help is not available, and then continue performing compressions until emergency services arrive with Automated External Defibrillator (AED).  Based on the recent studies, external compressions can be as effective as combinations of compressions and mouth-to-mouth.