OBJECTIVES: Our objective was to evaluate the short-term safety and efficacy of cardiac resynchronization therapy (CRT) in children. BACKGROUND: Cardiac resynchronization therapy has been beneficial for adult patients with poor left ventricular function and intraventricular conduction delay. The efficacy of this therapy in the young and in those with congenital heart disease (CHD) has not yet been established. METHODS: This is a multi-center, retrospective evaluation of CRT in 103 patients from 22 institutions. RESULTS: Median age at time of implantation was 12.8 years (3 months to 55.4 years). Median duration of follow-up was four months (22 days to 1 year). The diagnosis was CHD in 73 patients (71%), cardiomyopathy in 16 (16%), and congenital complete atrioventricular block in 14 (13%). The QRS duration before pacing was 166.1 ± 33.3 ms, which decreased after CRT by 37.7 ± 30.7 ms (p < 0.01). Pre-CRT systemic ventricular ejection fraction (EF) was 26.2 ± 11.6%. The EF increased by 12.8 ± 12.7 EF units with a mean EF after CRT of 39.9 ± 14.8% (p < 0.05). Of 18 patients who underwent CRT while listed for heart transplantation, 3 improved sufficiently to allow removal from the transplant waiting list, 5 underwent transplant, 2 died, and 8 others are currently awaiting transplant. CONCLUSIONS: Cardiac resynchronization therapy appears to offer benefit in pediatric and CHD patients who differ substantially from the adult populations in whom this therapy has been most thoroughly evaluated to date. Further studies looking at the long-term benefit of this therapy in this population are needed.