Tachyarrhythmias can occur at any age from the developing fetus through adulthood. However, in deference to adult-onset ischemic cardiac issues, abnormal heart rhythms occurring in the young are often due to developmental alterations of the cardiac conduction tissue, genetically-inherited changes of myocardial cellular ion membrane properties and both pre- and post-surgical repair of associated structural congenital heart anatomical defects. And different from adults, abnormal rhythms occurring in the young can spontaneously disappear with progressive patient growth. Both supra- and ventricular tachyarrhythmias occur in the young although atrial rhythm abnormalities far exceed those of the ventricle. In both, pharmacologic therapies to alter tissue conduction and refractoriness remain the mainstay for initial intervention in the infant and young child, reserving more invasive and potentially harmful ablation therapies for drug-refractory cases. The purpose of the review is to present common and uncommon tachyarrhythmias which can occur in the fetus and throughout infancy. Emphasis will be placed on their electrocardiographic identification, recognition of any associated structural congenital heart defects and recommended pharmacologic management. Drug therapies will be divided according to mechanism of action and discussions of which particular agent is potentially best-suited to treat which specific tachyarrhythmia. A listing of current pharmacologic agents used in the young with appropriate dosages is included.