Transvenous pacing has become the preferred method of pediatric cardiac pacing. Although no clinically important venous thromboses have been reported, concern has arisen about occult venous thrombosis. We evaluated 19 randomly selected children who had transvenous pacing implants. Sixteen were evaluated by venous plethysmography and Doppler while three had venous angiography and one had both. The leads had all been inserted by subclavian vein puncture. Ages at time of implant ranged from 17 months to 25 years; mean 9.8 years, median 9.0 years. Implant weights were from 9.6 kg to 56.0 kg, mean 31 kg, median 31 kg. The interval from implant to time of procedure ranged from 1 month to 46 months, mean 22.5 months, median 24 months. Four patients had one lead while 14 had two and one had four. Eleven leads were unipolar and 25 were bipolar. The bipolar leads were 6.6 French diameter. In the 19 patients evaluated, no thromboses were detected nor any narrowing greater than 10% of proximal diameter as seen by angiography. No disturbances of blood flow in the subclavian vein was noted. Transvenous pacing did not result in venous flow abnormalities in these pediatric patients.