The title suggests the passenger has died, the narrative merely says hes had a heart attack and is in poor shape.
If I was told a pax had suffered a heart attack I'd be returning or diverting.
I wouldn't be waiting for a doctor to certify he had died (if one was on board) as minutes could matter. I'd get on with it declaring a Mayday for a medical emerg. If a doctor subsequently certifies the patient as dead then the decision would be re assessed.