Ascending aortic dilatation (AoD) in patients with structurally normal hearts and congenital heart block (CHB) has been previously described. The cause and management of AoD are yet to be determined. The aim of this study was to test the hypothesis that AoD in children with CHB regresses after the implantation of cardiac dual-chamber pacemakers (PMs). The secondary hypothesis was an association between the presence of maternal antibodies (SS-A or SS-B) and the degree of aortic dilatation. Clinical data with echocardiographic correlates of patients with CHB followed at a single institution were retrospectively reviewed. Comparison of the target structures diameter was based on 3 different z-score equations, with AoD defined as a z score >2. Inclusion criteria were CHB diagnosis by 12-lead electrocardiography or Holter recording and benefit from a permanent dual-chamber PM. Excluded were patients with incomplete echocardiographic measurements, those with major structural heart defects, and those with syndromes or diseases known to be associated with AoD. There were 17 patients, diagnosed at a median age of 6 months (interquartile range 0 to 47.8). Maternal antibodies were positive in 6 patients and negative in 11. All patients underwent PM implantation at a median age of 4.5 years (interquartile range 1.4 to 7.9). AoD (z score >2.0 according to 3 different equations) was present in 35% to 59% of patients. There was a significant reduction of mean ascending aortic z score in patients with AoD from 4.66 to 3.67 (p = 0.06), from 4.82 to 2.95 (p = 0.002), and from 6.07 to 3.39 (p = 0.006) according to the various z-score equations. Most patients with positive serology had AoD, without reaching statistical significance. In conclusion, AoD is associated with CHB, more likely in infants exposed to maternal antibodies. AoD decreases after the implantation of a PM. This is probably related to the regularization of stroke volume.