How long can one survive without a heartbeat?Difficult one this! The common perception is 3-4 minutes but we had a patient a while ago who went into cardiac arrest shortly after arriving. After several cycles of CPR, a decision was taken to discontinue the resuscitation ( and the heart was scanned to confirm that there was no cardiac activity)
To our amazement ( horror!) the patient continued to take the occasional gasping breath for the next 20 minutes.
There is also the notion within Emergency Medicine, that you are not dead until you are 'warm and dead' so there are relatively frequent cases of resuscitation continuing for many hours in patients who are extremely cold. There are many documented cases of children particularly being revived after very long periods of time ( obviously CPR must continue)