© 2017 Elsevier B.V. Aim Estimate prevalence of ECPR-eligible subjects in a large, North American, multi-center cohort, describe natural history with conventional resuscitation, and predict optimal timing of transition to ECPR. Methods Secondary analysis of clinical trial enrolling adults with non-traumatic OHCA. Primary outcome was survival to discharge with favorable outcome (mRS 0–3). Subjects were additionally classified as survival with unfavorable outcome (mRS 4–5), ROSC without survival (mRS 6), or without ROSC. We plotted subject accrual as a function of resuscitation duration (CPR onset to return of spontaneous circulation (ROSC) or termination of resuscitation), and estimated time-dependent probabilities of ROSC and mRS 0–3 at discharge. Adjusted logistic regression models tested the association between resuscitation duration and survival with mRS 0–3. Results Of 11,368 subjects, 1237 (10.9%; 95%CI 10.3–11.5%) were eligible for ECPR, Of these, 778 (63%) achieved ROSC, 466 (38%) survived to discharge, and 377 (30%) had mRS 0–3 at discharge. Half with eventual mRS 0–3 achieved ROSC within 8.8 min (95%CI 8.3–9.2 min) of resuscitation, and 90% within 21.0 min (95%CI 19.1–23.7 min). Time-dependent probabilities of ROSC and mRS 0–3 declined over elapsed resuscitation, and the likelihood of additional cases with mRS 0–3 beyond 20 min was 8.4% (95%CI 5.9–11.0%). Resuscitation duration was independently associated with survival to discharge with mRS 0–3 (OR 0.95; 95%CI 0.92–0.97). Conclusion Approximately 11% of subjects were eligible for ECPR. Only one-third survived to discharge with favorable outcome. Performing 9–21 min of conventional resuscitation captured most ECPR-eligible subjects with eventual mRS 0–3 at hospital discharge.