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
Former Conservative party chairman says the mistakes of two Tory Prime Ministers in row have had "calamitous" consequences for Britain.
A 42-year-old woman has been held after at least six people were injured in a collision with a car outside a sports centre in Newcastle.
The Brexit Secretary's comments come after Chancellor Philip Hammond's remarks that no EU deal would "very, very bad" for the UK.