BACKGROUNDChanges in the fetal heart rate occur in approximately 1% of all pregnancies and in an autoimmune context with positive anti-Ro/ SSA and anti-La/SSB antibodies, the incidence is estimated to be 2-4%. The involvement of neonatal organs, especially heart and skin, is presumed to result from the transplacental passage of these antibodies. It is important to rule out undiagnosed maternal connective tissue diseases, such as systemic lupus erythematosus, Sjögren's syndrome, mixed connective tissue disease and leukocytoclastic vasculitis. The case presented shows an asymptomatic mother that had no criteria to any connective tissue diseases or any other pathologies, and became aware of these antibody reactivities solely based upon the finding of a bradyarrhythmia in her fetus. CASE REPORTA 28-year-old primigravida, with a singleton pregnancy of 25 weeks and without comorbidities, arrived at the rheumatology outpatient clinic referred by the obstetrician due to fetal bradycardia with a heart rate of 55-59 bpm verified on fetal echocardiogram performed 3 days ago. The patient denied any symptoms or previous diagnoses and did not use any medication or drugs. After performing laboratory tests, anti-Ro/SSA antibodies were detected in high titers (> 240) and anti-La/SSB in lower titers (30). Thus, hydroxychloroquine and betamethasone were started. After one week, the patient returned for consultation with a new echocardiogram showing complete atrioventricular block. Due to good fetal development, the pediatric cardiologist opted to indicate the placement of a pacemaker after birth. At 32 weeks of gestation, it was decided to discontinue betamethasone and maintain hydroxychloroquine. At 45 days of birth, the newborn underwent pacemaker placement. Currently, the patient remains asymptomatic, in follow-up and without the use of any medication, as well her son. CONCLUSIONThe prenatal diagnosis of the ethology of conceived heart diseases allows early treatment and the guarantee of intrauterine development. This will allow not only treatment during pregnancy, but also delivery assistance to these pregnant women in a tertiary perinatal center with a multidisciplinary team trained in the care of these infants and the implantation of a pacemaker, which is necessary in two thirds of cases. There is presence of bradycardia, ventricular dysfunction and the prolongation QT complications in these cases. Therefore, an accurate diagnosis of the etiology of fetal heart block is very necessary.