Although the long-term prognosis of children with persistent supraventricular tachycardia (SVT) has been generally considered benign, recent reports have suggested that some of these patients may develop cardiac dysfunction secondary to their persistent SVT. The clinical course of six children demonstrating ECG criteria of persistent SVT are presented herein with follow-up data for 5 to 20 years. Persistent SVT was present in each patient from 2 to 19 years. Two patients had transient congestive heart failure early in their course of persistent SVT, and two others demonstrated continued roentgenographic evidence of mild cardiomegaly without associated symptomatology. Conventional antiarrhythmics administered briefly in five patients and chronically in two were without effect on their arrhythmias. Persistent SVT remains in three patients and a fourth continues to exhibit intermittent episodes of SVT; however, all six patients are currently asymptomatic with two in stable normal sinus rhythm. This investigation indicates that the persistent form of SVT (lasting more than 1 year) is uncommon among children with paroxysmal SVT, and long-term observation of the consequences of persistent SVT supports the view that this rhythm disturbance is generally well tolerated in such patients.