Eighteen consecutive cases of fetal tachycardia referred to the department of Pediatric Cardiology, Uppsala University, were studied retrospectively. All cases were detected at a routine visit at an antenatal clinic. None of the cases had a structural heart disease. Fetal supraventricular tachycardia was found in 8 cases and atrial flutter in 10 cases. In 7 cases, hydrops and heart failure were diagnosed. Antenatal treatment with digoxin, alone or in combination with other antiarrhythmic drugs, was needed in 15 cases. In 10 cases an obvious effect of the therapy was observed. No intrauterine deaths occurred. One infant died postnatally. At birth, 4 infants were in need of neonatal intensive care when delivered. Antiarrhythmic treatment was started in 13 cases postnatally. Late relapse of tachycardia was reported in 3 children. In 1 of these cases the prenatal tachycardia had resolved spontaneously and the infant was not treated antenatally nor during the neonatal period. Although fetal tachycardia is a serious condition, antenatal treatment in combination with careful monitoring and induction of delivery in cases with deteriorating fetal condition result in a satisfactory outcome for the majority of infants. However, there is a risk of late recurrence.