OBJECTIVES--To determine the causes and outcome of residual shunting after transcatheter occlusion of persistent ductus arteriosus with the Rashkind double umbrella occluder, and to determine the potential of the device to produce obstruction to flow in the aorta and left pulmonary artery. DESIGN--Angiographic examination of morphology of ductus followed by prospective clinical and ultrasound evaluation (including cross sectional imaging, colour flow mapping, and pulse wave Doppler) of all patients undergoing occlusion of persistent ductus arteriosus between October 1987 and July 1992. PATIENTS--140 patients with ages between 0.5 and 78 (median 3.8) years and weights between 6.8 and 74 (median 13.8) kg. INTERVENTIONS--Attempted implantation of the Rashkind double umbrella ductus occluder under angiographic control through a transvenous (n = 136) or transarterial (n = 4) approach. MAIN OUTCOME MEASURES--Successful occlusion of ductus; frequency, pattern, and prognosis of residual shunts; Doppler velocities in left pulmonary artery and aorta; volume loading of the left heart. RESULTS--Including reocclusions the overall rate of successful occlusion was 96%. A total of six devices embolised at the time of operation (4.3%) with no sequelae. There were no anatomical factors that predicted a poor outcome, but suboptimal positioning of the device led to a significantly higher incidence of residual shunts (p < 0.001). Colour flow mapping correctly identified shunts that were unlikely to close spontaneously (n = 9) and to date seven have undergone successful closure with a second device. Encroachment of device legs produced statistically (p < 0.001) but not clinically significant increases in left pulmonary artery Doppler velocities that diminished with time. CONCLUSIONS--Transcatheter occlusion provides a safe and effective means of closing a persistent ductus arteriosus. Doppler colour flow mapping is necessary for follow up and shows those ducts requiring reocclusion. The device did not produce significant disturbance to flow in the pulmonary arteries or aorta.