Hemodynamic effects of propranolol in 23 Patients with congenital heart disease were studied at cardiac catheterization. Fifteen cases with pulmonary stenosis showed elevation of pulmonary artery pressure and depression of right ventricular pressure, maximum dp/dt of right ventricle and blood pressure with statistic significants after propranolol injection. In 4 cases with marked elevation of pulmonary artery pressure without significant change of right ventricular pressure, localized muscular stenosis of right ventricular outflow tract without valvular or severe valve ring stenosis were proved by surgery. Propranolol would be usefull to know the nature of pulmonary stenosis.