(CNN) -- Chris Brooks, just 22, was out for a night of bowling with friends. Exhausted, on the way home, he texted his girlfriend, "I'm dead." Fifteen minutes later, he was -- clinically dead -- suffering an unexplained cardiac arrest on the couch at home, right in front of his parents. But it wasn't the end.
The same night Chris Brooks died, he came back to life. Doctors say that for every minute without a heartbeat, your odds of survival go down 10 percent. Chris Brooks was out for more than 20 minutes -- and yet he survived, without even a hint of brain damage.
Doctors at the University of Pennsylvania's Center for Resuscitation Science, where Brooks was treated, call him a medical miracle -- but cases like his are increasingly common, thanks to advances in basic emergency techniques including improved CPR and cooling patients to a lower body temperature. Here's the catch: Many hospitals and doctors don't know or want to use the latest techniques -- and so survival rates for cardiac arrest vary tenfold among major cities.