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Due to a low heart rate (HR) in children with congenital complete atrioventricular block (CCAVB), a larger stroke volume of the left ventricle (LV) may be expected. If so, end-diastolic (LVEDD) and end-systolic (LVESD) diameters may be enlarged and even dilated cardiomyopathy (DCM) may occur. The aim of this study was to answer the question if children with CCAVB develop LV dilatation. Furthermore, we investigated whether LV dilatation would decrease after pacing.We longitudinally evaluated echocardiographic data (LVEDD, LVESD, shortening fraction [SF]) in 36 children with CCAVB. Age at the first visit was 2.5 ± 3.3 years (mean ± SD); follow-up 10.6 ± 7.3 years.Three children had DCM, already at 1st visit. LVEDD and LVESD Z scores in all children with CCAVB were larger than in normal controls (LVEDD Z score 1.38 ± 1.80; LVESD Z score 0.64 ± 1.35). Both Z scores were larger when HR was lower. Both Z scores increased over time in children who met criteria for pacing, but did not change in non-paced children. Physiologic pacing decreased both Z scores. SF of all children was normal and remained normal during follow-up (0.39 ± 0.05 1st visit vs 0.39 ± 0.06 last visit).We conclude that children with CCAVB have LV dilatation, which is progressive in children who met criteria for pacing. LV dilatation regressed by physiologic pacing. LV dilatation was larger when HR was lower. SF does not deteriorate over time. DCM occurs early in the disease and does not develop during childhood, not even in children with LV dilatation.