Pulmonary arteriovenous fistulas (AVFs) are a rare but recognized cause of cyanosis in childhood. Lesions may be acquired as in hepatopulmonary syndrome or they may be congenital, particularly in association with certain multisystem disorders. Large fistulas are more common than multiple small connections. Two cases. both boys, presenting in the first decade of life are described. "Bubble" echocardiography was the most telling investigation and strongly suggested the presence of AVFs in both cases. Each patient then underwent cardiac catheterization, which demonstrated normal pulmonary artery pressure and diffuse pulmonary telangiectasis. Both patients were treated effectively with nifedipine and continue with this mode of therapy.