A 3-year-old child with a patent arterial duct underwent percutaneous transcatheter occlusion using Rashkind's "double umbrella" technique. The procedure, using a 17 mm device, was uncomplicated. An echocardiogram done 6 hr later showed a mobile 5 x 3 mm thrombus on the pulmonary aspect of the device. The thrombus resolved after 24 hr of intravenous heparin.