a. At least 1 branch pulmonary artery stenosis referred for planned catheterization for PA dilation b. At least one of the following: i.greater than one half systemic right ventricular pressure ii. regional decrease in pulmonary blood flow by lung scan iii. elevated pulmonary artery pressures (> 20 mmHg MPAP) iv. cyanosis at least in part due to PA stenosis c. Informed consent of patient and/or parent/guardian; assent of mature minors d. Agreement to participate in protocol, including follow-up testing