The objective of this study was to determine whether arrhythmia in the setting of maternal cardiac disease (MCD) affects perinatal outcomes.This is a retrospective cohort study of pregnant women with MCD who delivered during 2008 to 2013. Perinatal outcomes among women with an arrhythmia were compared with those without.Among 143 women, 36 (25%) had an arrhythmia. Those with an arrhythmia were more likely to have a spontaneous vaginal delivery (64 vs 43%, P<0.05) and required fewer operative vaginal births (8 vs 27%, P=0.02). Pregnancies were more likely to be complicated by intrauterine growth restriction (IUGR) (17 vs 5%, P<0.05), although there were no differences in the rate of small for gestational age. The risk of IUGR remained increased after controlling for confounding (adjusted odds ratio 6.98, 95% confidence interval 1.59 to 30.79, P=0.01). Two cases of placental abruption were identified among mothers with arrhythmia while none were identified in the controls (P<0.05).Patients with arrhythmias were more likely to have a spontaneous vaginal delivery. Our data suggest that these pregnancies were an increased risk for IUGR.