Objective: We aimed to describe a single institutional experience managing tachyarrhythmic fetuses, to investigate the underlying pathological findings and to evaluate the postnatal follow-up results. Method: This retrospective study included 24 fetuses, treated and followed up with the diagnosis of supra -ventricular tachyarrhythmia between January 2014 and July 2020. Fetal tachyarrhythmia was evaluated by M mode and Doppler ultrasound. Patients were divided into two categories, fetuses with supraventricular tachycardia (SVT) and those with atrial flutter. Also, patients with SVT were subgrouped as short ventriculo-atrial (VA) SVT and long VA SVT. The presence of hydrops was recorded. Prenatal and postnatal data were all collected from hospital records. Results: SVT and atrial flutter were diagnosed in 23 fetuses and in one fetus, respectively. Of the 23 fetuses with supraventricular tachycardia, 12 cases had short VA time interval and 11 had long VA time interval. Antiarrhythmic therapy was applied to 19 cases, but was not initiated in five cases. Thirteen cases responded to single antiarrhythmic drug. Seven (88%) out of 8 cases with short VA SVT without any sign of hydrops responded to digoxin as a single therapy. Six (67%) out of 9 cases with long VA SVT responded to single ther-apy. In 6 cases (including atrial flutter), combined antiarrhythmic drug was required. In only one fetus, SVT (long-VA) did not convert to sinus rhythm despite high dose combined antiarrhythmic therapy. Six fetuses (25%) had signs of hydrops. In hydrops cases, overall fetal and neonatal mortality rate was 33%. In the absence of hydrops the mortality rate was zero. Second or third line antiarrhythmic treatment options were required in 83% (5 cases) of hydropic fetuses, whereas in only 8% (one case) of non-hydropic cases. Only one fetus recurred. Maternal complications due to antiarrhythmic therapy developed in four cases. Postnatal antiar-rhythmic therapy was required in seven cases. Conclusion: We found that in the absence of hydrops, all tachycardiac fetuses responded to treatment regardless of the treatment option. In cases with hydrops, mortality was not observed when anti-arrhythmic treatment was started before significant cardiac dysfunction and heart failure. The need for postnatal treatment was com -mon among those with recurrent tachyarrhythmia under treatment, recurrent arrhythmia after discontinuation of fetal therapy, arrhythmia followed up without treatment in the late gestational period and arrhythmias such as Junctional ectopic tachycardia (JET) and Wolff-Parkinson-White syndrome (WPW) syndrome. (c) 2022 Elsevier Masson SAS. All rights reserved.