Introduction: Complete heart block (third-degree atrioventricular block) is a defect of the conduction system of the heart, in which the impulse generated in the sinoatrial node does not propagate to the ventricles, and thus the latter contract independently of the atria. A third-degree atrioventricular block can be either congenital or acquired. In 60-70% of the cases, the congenital heart block results from destruction of the conduction system of the fetal heart by anti-Ro/SSA and anti-La/SSB antibodies present in maternal serum. The antibodies are synthesized in the course of autoimmune maternal conditions, most often systemic lupus erythematosus or, rarer, rheumatoid arthritis, dermatomyositis or Sjögren’s syndrome. The complete block can occur as an isolated defect or be associated with structural anomalies of the fetal heart. Material and methods: A total of five patients whose fetuses were diagnosed with the third-degree atrioventricular block have been hospitalized at the Department of Obstetrics, Medical University of Gdansk between 2012 and 2014. Results: We present the data of the five patients, hospitalized at the Department of Obstetrics, Medical University of Gdansk, whose fetuses were diagnosed prenatally with the complete heart block. The cases differ in terms of etiology, clinical outcome, and postnatal treatment. All data are presented in Table I. Conclusions: We emphasize the role of appropriate pregnancy management and careful monitoring of the fetal condition. From obstetrical perspective, it is important to monitor the condition of fetuses with the third-degree atrioventricular block ultrasonographically and echocardiographically; in turn, cardiotocography is less useful in this setting. Therefore, a non-reactive cardiotocographic tracing should not constitute an indication for a preterm delivery. An affected fetus should be delivered in a tertiary center for perinatal care that cooperates with a pediatric cardiology center. An efficient program for cardiologic prenatal care and close cooperation between obstetricians, neonatologists, pediatric cardiologists, and cardiac surgeons constitute the key to a successful outcome.