Progressive stenosis of the semilunar valves in utero can be life threatening. We treated two fetuses with complete or almost complete pulmonary atresia and imminent hydrops (increased cardiothoracic ratio, pericardial effusion, holosystolic tricuspid regurgitation extending into diastole, and abnormal venous Dopplers). We dilated the pulmonary valve of two fetuses in utero at 28 and 30 weeks' gestation, through the mothers' abdomens. After the procedure, the fetuses had decreased signs of circulatory failure and gestation continued until near term. In the neonatal period, we did a repeat valvuloplasty with systemic-to-pulmonary arterial shunt. Both children (now aged 18 months and 12 months) now have biventricular circulation. Surgery on selected fetuses with semilunar valve stenosis or atresia, or both, can extend pregnancy and favourably change the postnatal surgical options.