Traditional methods of identifying partial anomalous pulmonary venous connection to the right atrium in the presence of an atrial defect are not always reliable. Twenty patients were studied with a new technique in which the catheter is introduced into the right superior pulmonary vein followed by echocardiographic assessment of the catheter position in relation to the left atrium and atrial septum. The insertion site of the right pulmonary veins was detected in every patient and in ten patients has been verified at operation. This approach can be performed rapidly and appears to be accurate as well as reliable.