Study research questions will address the following: OHCA incidence in different European regions; incidence of cardiopulmonary resuscitation (CPR) attempted; initial presenting rhythm in patients where bystanders or EMS starts CPR or any other resuscitation intervention; rate of any return of spontaneous circulation (ROSC); patient status at handover to a hospital i.e. ROSC, ongoing CPR, dead; incidence of patients still alive 30 days after OHCA; incidence of patients discharged alive from hospital.