Background Untreated isolated fetal complete atrioventricular block(CAVB) has a significant mortality rate. A standardized treatment approach, including mate rnal dexamethasone at CAVB diagnosis and β stimulation for fetal heart rates<5 5 bpm, has been used at our institutions since 1997. The study presents the impa ct of this approach. Methods and Results Thirty seven consecutive cases of fet al CAVB since 1990 were studied. Mean age at diagnosis was 25.6±5.2 gestational weeks. In 33 patients (92%), CAVB was associated with maternal anti Ro/La aut oantibodies. Patients were separated into those diagnosed between 1990 and 1996 (group 1; n=16) and those diagnosed between 1997 and 2003 (group 2; n=21). The 2 study groups were comparable in the clinical presentation at CAVB diagnosis but did differ in prenatal management (treated patients: group 1, 4/16; group 2, 18 /21; P< 0.0001). Overall, 22 fetuses were treated, 21 with dexamethasone and 9 w ith β stimulation for a mean of 7.5±4.5 weeks. Live birth and 1 year surviv al rates of group 1 were 80%and 47%, and these improved to 95%for group 2 pat ients (P< 0.01). The 21 patients treated with dexamethasone had a 1-year surviv al rate of 90%, compared with 46%without glucocorticoid therapy (P< 0.02). Imm une mediated conditions (myocarditis, hepatitis, cardiomyopathy) resulting in p ostnatal death or heart transplantation were significantly more common in untrea ted anti Ro/La antibody associated pregnancies compared with patients treated with steroids (0/18 versus 4/9 live births; P=0.007). Conclusions -A standardiz ed treatment approach, including transplacental fetal administration of dexameth asone and β stimulation at heart rates< 55 bpm,reduced themorbidity and improv ed the outcome of isolated fetal CAVB. A standardized treatment approach, including mate rnal dexamethasone at CAVB diagnosis and β stimulation for fetal heart rates <5 5 bpm, has been used at our institutions since 1997. The study presented the impa ct of this approach. Methods and Results Thirty seven consecutive cases of fet al CAVB since 1990 were studied. Mean age at diagnosis was 25.6 ± 5.2 gestational weeks. In 33 patients (92%), CAVB was associated with maternal anti Ro / La aut oantibodies. Patients were separated into those diagnosed between 1990 and 1996 (group 1; n = 16) and those diagnosed between 1997 and 2003 (group 2; n = 21). The 2 study groups were comparable in the clinical presentation at CAVB diagnosis but did not differ in prenatal management (treated patients: group 1, 4/16; group 2, 18/21; P <0.0001). Overall, 22 fetuses were treated, 21 with dexamethasone and 9 w ith β stimulation for a mean of 7.5 ± 4.5 weeks. Live birth and 1 year surviv al rates of group 1 were 80% and 47%, and these improved to 95% for group 2 patients (P <0.01). The 21 patients treated with dexamethasone had a 1-year surviv al rate of 90%, compared with 46% without glucocorticoid therapy (P <0.02). Imm une mediated conditions (myocarditis, hepatitis, cardiomyopathy) resulting in p ostnatal death or heart transplantation were significantly more common in untrea ted anti Ro / La antibody associated pregnancies compared with patients treated with steroids (0/18 versus 4/9 live births; P = 0.007). Conclusions -A standardiz ed treatment approach, including transplacental fetal administration of dexameth asone and beta stimulation at heart rates <55 bpm, reduced themorbidity and improv ed the outcome of isolated fetal CAVB.