The incidence, manifestation and management of arrhythmia in congenital heart disease (CHD) during pregnancy were evaluated in a multicenter study. Of 126 pregnancies in patients with CHD in 17 institutions from January 1991 to December 2000, 29 cases of pregnancy in 27 patients after cardiac repair (mean age, 29+/-4.9 years) were identified with arrhythmias (supraventricular tachyarrhythmia (SVT) in 15, ventricular tachycardia (VT) in 9, high-grade atrioventricular block in 4 and sick sinus syndrome in 3) (group A) and 29 control pregnancies from 29 patients with repaired CHD and no arrhythmias (group B). SVT tended to require anti-arrhythmic medication more than VT (10/15 vs 2/9, p=0.04). Nine different types of anti-arrhythmic agents were successfully administered without maternal complications. There were no maternal deaths in either group. In the comparison of group A with group B, there was lower cardiac functional class (8/29, p=0.04), higher incidence of polysplenia (4/29, p=0.04), and higher incidence of low-birthweight infant (7/29, p=0.02) in the former. It appears that there is a high prevalence of arrhythmias during pregnancy in patients with repaired CHD. Patients with CHD and low cardiac functional class and/or polysplenia could have arrhythmia during pregnancy that results in a low-birthweight infant. Meticulous care for these patients during pregnancy is recommended.