OBJECTIVE--To assess the efficacy of arterial duct angioplasty in maintaining adequate ductal patency in neonates with critical pulmonary valve stenosis. PATIENTS--Two neonates presenting with cyanosis due to critical pulmonary valve stenosis with severe right ventricular hypoplasia underwent percutaneous balloon dilatation of the pulmonary valve. Despite successful dilatation, both remained cyanosed while receiving prostaglandin E2 infusions. RESULTS--Angioplasty of the arterial duct resulted in increased arterial oxygen saturations. Adequate arterial duct patency was maintained for three months during which time right ventricular dimensions increased enough to allow sufficient pulmonary circulation without the duct. CONCLUSIONS--Arterial duct angioplasty is an effective additional treatment for patients with critical pulmonary valve stenosis whose right ventricle is too small to provide adequate forward flow after balloon dilatation of the valve. Arterial duct angioplasty sustains adequate patency of the duct while the right ventricle grows sufficiently to undertake the pulmonary circulation.