OBJECTIVE: To investigate the spectrum of pulmonary atresia and critical pulmonary stenosis using right ventricular outflow tract angiography and explore its implications for catheter interventional treatment. DESIGN: Prospective clinical study. SETTING: Two paediatric cardiology centres. SUBJECTS: 11 neonates or infants (aged 1 day to 8 months; weighing 2.3 to 7.8 kg) with pulmonary atresia or where the differentiation of pulmonary atresia from critical pulmonary stenosis was unclear on either echocardiography or angiography. METHODS: Right ventricular outflow tract angiography was performed on all patients to distinguish pulmonary atresia from critical pulmonary stenosis before opening the right ventricular outflow tract. RESULTS: Right ventricular outflow tract angiography showed that three of seven patients diagnosed as pulmonary atresia by echocardiography had pin hole jets across the pulmonary valve; another had a probe patent valve that appeared imperforate on both echocardiography and right ventricular outflow tract angiography. Three of the four patients diagnosed by echocardiography as critical pulmonary stenosis were found on right ventricular outflow tract angiography to have pulmonary atresia. The remaining patient had such a tiny orifice that a second orifice had to be created with a radiofrequency catheter. The right ventricular outflow tract was opened successfully in 10 of the 11 patients, six of whom required application of radiofrequency energy. The right ventricular to aortic systolic pressure ratio fell from 1.4 (0.9 to 1.9) to 0.6 (0.2 to 1.1) (P < 0.05). All 11 patients were alive and well with transcutaneous oxygen saturations ranging from 84% to 95% at a median follow up duration of nine months. CONCLUSIONS: Critical pulmonary stenosis and pulmonary atresia cannot always be accurately distinguished by echocardiography. Right ventricular outflow tract angiography helps to distinguish the two groups. In most cases the right ventricular outflow tract can be opened without mortality and with short to medium term survival.