For those of us who know CPR, there are new guidelines out from the American Heart Association that change the number of chest compressions from 15 to 30 between the two breaths that you give. My certification has long since lapsed, but I imagine it's time to take a class again, once they are teaching the updated curriculum. Thankfully, I've never had to use CPR on anyone but the teaching dummies.
Studies show that the chest compressions create more blood flow through the heart to the rest of the body, buying time until a defibrillator can be used or the heart can pump blood on its own. Studies have also shown that blood circulation increases with each chest compression and must be built back up after an interruption, the association says in its online journal Circulation.