Two cases of foetal supraventricular tachycardia with hydrops with fatal outcomes illustrate the poor general prognosis of this condition. The absence of therapeutic consensus, of large series in the existing literature, does not prevent logical and reasonable management based on rhythmological, pharmacological and prognostic criteria. A combined approach associating antiarrhythmic therapy by the transplacental and intrafunicular approaches seems acceptable now that funicular puncture can be undertaken easily, and certain antiarrhythmic molecules suggest encouraging results. It is important to try to assess the haemodynamic tolerance by foetal Doppler echocardiography because the foetal prognosis depends on ischaemic cerebral lesions induced by anoxia, difficult to diagnose in utero: when observed, aggressive and occasionally dangerous therapies to foetus and mother may be justified in these extreme situations of foetoplacental hydrops.