The East Anglian Air Ambulance was called to Eaton Park in Norwich this afternoon after a man collapsed.
Emergency services were called to the park - which was packed with people making the most of the warm weather - at 1.11pm on Saturday.
The first paramedic was at the scene within three minutes of the initial call. When they arrived two off duty doctors were already helping the man.
The East of England Ambulance Service sent an ambulance crew, an ambulance officer and a rapid response vehicle. The East of England Air Ambulance was also dispatched. Norfolk police also attended.
The man, believed to be in his 40s, had suffered a cardiac arrest and was not breathing when paramedics first arrived, but they managed to resuscitate him at the scene.
He was taken to the Norfolk and Norwich University Hospital by land ambulance for further treatment and was in a stable condition.
An eye-witness witness said he saw paramedics giving emergency treatment to the patient.
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