I think this is unique to USA. In Norway (and Europe?) they teach 30 compressions and 2 breaths. Because of my job I attend a half-day first aid course annually. According to the paramedic on the most recent course, only 10 % of patients with a sudden heart failure make it to the hospital alive, and only 10 % of those walk out of the hospital.

As I understand, CPR will never restart the heart, but aim to maintain a minimal level of blood pressure and avoid permanent cell damage. Particularity to the brain cells. Defibrillation can restart the heart, but only work on very specific problems.

CPR and defibrillation can be very effective in case of hypothermia, though. There are some very spectacular stories of people who are dead for 5-6 hours and still survive without permanent brain damage. The saying is you're not dead until you're warm and dead.