Two children with exercise-induced tachycardia, one with idiopathic long-QT syndrome, are presented. The patients were evaluated by exercise testing and electrophysiologic study. From the onset of treatment with the beta-blocking agent, pindolol, the patients have been symptom-free. These findings emphasize that children with syncope must be evaluated by ECG, exercise testing, 24-h Holter-monitoring, and finally, electrophysiological study.