Heart failure patients will be unable to give their consent to take part in a trial where they will be given a placebo rather than a standard adrenaline shot.
However, the study has been approved by the Oxford Research Ethics Committee and is funded by the National Institute for Health Research.
The first 8,000 patients to suffer a cardiac arrest out of hospital will form the sample for the trial, which will begin in Wales, the West Midlands, North East, the south coast and London this autumn.
"Adrenaline is an unproven treatment for cardiac arrest, which is why there is a need for this study.
The study is referred to as a 'double blind trial', as neither the patient nor the paramedic, nurse or doctor will know in which treatment group someone was in.
It is not possible to obtain consent in the immediate emergency situation as resuscitation must be started without delay. A member of the research team will seek consent to continue in the study as soon as possible once the initial emergency has passed."
More top news
A US doctor has been accused of killing a lion during an illegal hunt, a week after it emerged dentist Walter Palmer killed Cecil the lion.
Mostly dry overnight in the east, strong winds and showery rain affecting Scotland & Northern Ireland
A couple have got married for the second time after the bride forgot their first big day following a car crash.