Abstract Introduction Survival from refractory out of hospital cardiac arrest (OHCA) without timely return of spontaneous circulation (ROSC) utilising conventional advanced cardiac life support (ACLS) therapies is dismal. CHEER3 was a safety and feasibility study of pre-hospital deployed extracorporeal membrane oxygenation (ECMO) during cardiopulmonary resuscitation (ECPR) for refractory OHCA in metropolitan Australia. Methods This was a single jurisdiction, single-arm feasibility study. Physicians, with pre-existing ECMO expertise, responded to witnessed OHCA, age