Long-QT syndrome is a rare, inherited cardiac channelopathy that is characterized by arrhythmia, syncope and sudden cardiac death. Foetal symptoms are very rare and prenatal diagnosis is difficult. We report on a foetal presentation of long-QT syndrome with severe hydrops and a chaotic heart rhythm at 32 weeks of gestation. Postnatal electrocardiography showed runs of polymorphic ventricular tachycardia and an extremely prolonged-QT segment (QTc of 640 ms). The initial approach of overdrive pacing, followed by the combined therapy of a beta blocker, a sodium channel blocker (mexiletine) and potassium suppletion proved successful in maintaining a stable sinus rhythm. The girl was doing well at eight months of followup. In this patient a timely diagnosis and effective management after birth have been life-saving.The intrauterine manifestation of foetal atrioventricular dissociation and ventricular arrhythmia should raise suspicion of congenital long-QT syndrome.