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Below are the ECGs of a newborn infant (39 weeks of gestational age) at three hours (left) and three days of life (right). Fetal supraventricular tachycardia was not controlled with maternal digoxin, but was well controlled with flecainide. Four maternal flecainide concentrations were obtained at 32–35 weeks’ gestation and ranged from 380–470 μg/l. Last concentration was 440 μg/l (therapeutic range 200–700 μg/l). Maternal ECGs were normal throughout. Following delivery at 39 weeks’ gestation, the baby’s flecainide concentration was very high (1030 μg/l) and the ECG showed a prolonged QRS duration (below left). By day 3 the QRS duration was normal (below right). The newborn was commenced on digoxin and there was no recurrence of the arrhythmia. There is no evidence that flecainide is concentrated in the fetus and the most likely explanation of the high neonatal flecainide was that the maternal concentration had increased very late in gestation. We strongly recommend that maternal flecainide concentrations need to be checked up to term, to avoid potential maternal and fetal toxicity.