Background: Patients with congenital complete atrioventricular block often require lifelong pacemaker therapy, which has a risk of left ventricular (LV) dysfunction. The aim of our study was to determine the long-term effects of epicardial pacing on LV function and dyssynchrony in children with congenital heart block. Methods: We conducted a retrospective study at a single tertiary center in which 34 pediatric patients with isolated congenital complete heart block who underwent epicardial pacemaker implantation from 1987 to 2016 were enrolled. Results: Median age during pacemaker insertion was 2.5 years (range, 0-16.7 years) and the median follow-up duration was 12.3 years. The initial pacing sites were the right ventricle (RV) free wall for 10 patients, RV apex for 16, and LV apex for eight. LV dysfunction developed in 7 patients, of whom 4 underwent lead relocation to the RV apex (n = 2) and cardiac resynchronization therapy upgrade (n = 2). RV free-wall pacing had a significantly higher risk of LV dysfunction than either LV or RV apical pacing (odds ratio 52.5; P = .003; 95% confidence interval 3.9-700). All 4 patients who underwent lead repositioning showed improvement of LV function (median ejection fraction, 24%-62.7%). Conclusions: Our study suggests that RV free-wall pacing may be a significant risk factor for LV dysfunction. Pacemaker-induced LV dysfunction was improved via lead relocation to the RV apex or cardiac resynchronization therapy upgrade. Future studies with a larger sample size and longer-term follow-up are required to confirm our results.