Arterial cannulation for constant monitoring of arterial pressure and blood gase analyses has become commonplace in the care of the critically ill patients. The radial artery is often regarded as causing a negligible complication risk because of extensive collateral arterial flow in the hand. One of other alternative sites for arterial cannulation is femoral artery. Femoral artery cannulation has a high degree of success in very small, critically ill children. It should be considered an acceptable alternative to small-vessel cannulation when the latter is not technically achievable, or in the unstable patient where rapid establishment of reliable artery access is necessary. Arterial cannulation may cause many complications: arterial catheters can directly injure the vessels, resulting in thrombosis, occlusion, distal embolization or ischemia. Local insertion site complications, such as hematoma, hemorrhage, and infection may occur. Arterial catheter may also be a source of systemic sepsis. We report an unusual case of unintentional release of a catheter fragment into the external iliac artery in a 7-month (7.8 kg) male patient with tetralogy of Fallot, which was inadvertently inserted during right femoral artery cannulation. The catheter fragment was successfully retrieved with the Amplatz Goose Neck microsnare under fluoroscopy without any problems.