15:2 was the previous standard, after the 5:1 which Tom mentions. It was part of the first international consensus on resuscitation in 2000. Research showed that for most people, oxygenation wasn't the issue (in a sudden cardiac arrest, there is still plenty of oxygen around for a while), but that getting it around was the problem, hence compressions being of more importance. However, it was also discovered that compressions could only give about 30% of the effectiveness of the heart actually beating, and we were only buildling up enough pressure to actually pump a significant amount of blood around after 10-12 compressions. In stopping to provide breaths (which in those days were given over a longer time-frame, and multiple attempts to get them in were encouraged, all of which increased the time compressions weren't being done), this pressure reduced to almost zero and had to be built up again when you restarted compressions. Hence you were getting maybe half a dozen decent compressions which actually pushed blood around per minute, as opposed to the 60-80ish you'd be getting if the heart was actually working. Hence the switch to 30 compressions - there was no scientific evidence for that number, it was seen as "more than 15" and "not enough to knacker you out". I'm yet to see a convincing study comparing survival rates for 30:2 vs 15:2, but like Tom I think the change has played a significant part in the increase in survival. Thanks must also go to other things though - public access defibrillation has been a god-send. In high-population/high-throughput areas such as train stations, airports, shopping centres etc., having a defib is rapidly becoming the norm. We're also seeing more and more rural areas set up community first responder schemes. Training for members of the public is improving drastically - the numbers of workplace first aiders trained each year is booming, and the HSE's proposal to regulate a shortened course covering basics such as CPR should improve this further. In addition, several large charities such as the British Heart Foundation, Royal Lifesaving Society, St John Ambulance and so on are offering training to schoolchildren, community groups, friends/family of those with heart conditions, and anybody else who is interested. The 8 minute response time target now means that ambulance services are pretty much bound to respond to these calls quickly too. On this point Tom and I disagree - there are lots of reasons why survival rates have improved, but one of them is this target. It encourages ambulance services to find more innovative ways to ensure that all calls are responded to quickly - FRUs, CFRs, motorbikes etc. all play an important part in this. We shouldn't kid ourselves that if this target didn't exist, things would be better for cardiac arrest victims - they absolutely would not.