Current organ allocation algorithms direct hearts to the sickest recipients to mitigate death while waiting. This may result in lower post-transplant (Tx) survival for high-risk candidates mandating close examination to determine the appropriateness of different technologies as a bridge to Tx. Methods and Results-We analyzed all patients (<18 years old) from the Pediatric Heart Transplant Study (PHTS) database listed for heart Tx (1993-2013) to determine the effect of extracorporeal membrane oxygenation (ECMO) support at the time of listing and the time of Tx on waitlist mortality and post-Tx outcomes. Eight percent of patients were listed on ECMO, and within 12 months, 49% had undergone Tx, 35% were deceased, and 16% were alive waiting. Survival at 12 months after listing (censored at Tx) was worse in patients on ECMO at listing (50%) compared with ventricular assist device at listing (76%) or not on ECMO or ventricular assist device at listing (76%; P<0.0001). Two hundred three (5%) patients underwent Tx from ECMO; 135 (67%) had been on ECMO since listing, and 67 (33%) had deteriorated to ECMO support while waiting. Survival after Tx was worse in patients who underwent Tx from ECMO (3 years: 64%) versus on ventricular assist device at Tx (3 years: 84%) or not on ECMO/ventricular assist device at Tx (3 years: 85%; P<0.0001). Patients transplanted from ECMO at age <1 year had the worst survival. Conclusions-Pediatric patients requiring ECMO support before heart Tx have poor outcomes. Prioritization of donor hearts to children waitlisted on ECMO warrants careful consideration because of ECMO's high pre-and post-Tx mortality.