Atrial flutter is a rare complication of the insertion of an umbilical venous catheter. We report a neonate who had an umbilical venous catheter placed within the first 24 hours of life and developed a hemodynamically stable tachyarrhythmia. The arrhythmia was successfully managed with synchronized cardioversion, with no further complications. The presentation and management are discussed. Physicians should be watchful for such potentially life-threatening complications from the placement of indwelling lines.