The authors report two cases of slow ventricular tachycardia presenting in the antenatal period. One foetus had anasarca at 38 weeks' gestation. After birth, improved myocardial function contributed to the rapid resorption of the effusions. The other case was well tolerated in the foetal and neonatal periods. In both cases, Holter ECG recorded an intermittent ventricular arrhythmia with salvos of sustained ventricular tachycardia with a maximum rate of 185/min, only 10% higher than the underlying sinus rhythm, disappearing on acceleration of the sinus rhythm. The aetiological investigation was negative. Therapeutic abstention was supported by the spontaneously favourable outcome after 3 and 5 months. Slow ventricular tachycardia or accelerated idioventricular rhythms are usually considered to be benign but the case with foetal anasarca suggests that they should be carefully followed up in the neonatal period. In the absence of a consensus on management, therapeutic abstention implies regular cardiological examination until the arrhythmia has disappeared.