Six cases of right external iliac and common femoral arterial thrombotic occlusions following transfemoral cardiac catheterization were found among the 117 infants and children with congenital heart disease. Physical findings of arterial thrombosis were lower extremity coldness and absence of femoral pulse, which appeared just after cardiac catheterization. Transcatheter local in trathrombotic infusion of Urokinase were done with 50000 IU bolus doses and 40000-50000 IU/h running doses. All 6 cases showed complete thrombolysis and re-establishment of femoral circulation. Three cases developed bleeding from arterial puncture sites, and were subsequently controlled properly by compression. No other complication was found. Our results suggest that local thrombolytic therapy with Urokinase is effective treatment method without significant complication for the infants and children with fresh thrombotic occlusion following cardiac catheterization and angiography.