OBJECTIVE To describe the presentation, diagnosis and treatment of fetal supraventricular tachyarrhythmias in a series of fetuses followed in a tertiary Fetal Cardiology Center. METHODS Twenty-five fetuses with diagnosis of supraventricular tachyarrhytmia were reported from January 1989 to October 1997, among 3117 pregnant women referred for fetal cardiac evaluation. RESULTS There were 17 fetuses with the diagnosis of supraventricular tachycardia (SVT) and 8 patients with atrial flutter (AF). Gestational age ranged from 26 to 40 weeks. Twelve patients were hydropic at presentation (6 with SVT and 6AF). Four fetuses with SVT showed structural abnormalities (two with Ebsten's anomaly and two with VSD). All patients were admitted to the Fetal Cardiology Unit for monitoring and treatment. Among 17 fetuses with SVT, twelve showed good response to digoxin administration, but this drug was not useful in any of the patients with flutter. In two patients with SVT and in six with AF, the pregnancy was interrupted to perform post-natal cardioversion. The mortality rate was 3/17 in the SVT group (including 2 patients with ebstein's anomaly and 0/8 in the flutter group) CONCLUSIONS Fetal supraventricular tachyarrithmias are rare in the general population. Nevertheless, the fetus may present with severe heart failure and death. Considering the satisfactory therapeutic response, accurate diagnosis and early treatment of these conditions are extremely important.