Pulmonary artery stenosis is a frequent complication seen after surgical repair of tetralogy of Fallot. In this setting, endovascular stent implantation is now accepted as the first-choice therapeutic option. However, angiographic imaging still being held as mandatory to check the stent position before final deployment, this procedure is not considered suitable for patients who cannot be submitted to angiography. In this paper, we report a novel method for the correct implantation of an endovascular stent without angiographic imaging. A 9-year-old boy underwent cardiac catheterization to relieve a severe left pulmonary artery stenosis. A previous attempt had been aborted due to a life-threatening anaphylactic reaction to the contrast medium. To avoid angiography, a contrast medium-filled compliant atrial septal defect sizing balloon (Amplatzer Sizing Balloon, AGA Medical Corporation) was used to image the vessel stenosis and successfully guide stent deployment. After the procedure, the transstenotic pressure gradient disappeared and the left-to-right pulmonary perfusion imbalance almost completely reverted.