[Exercise-induced tachyarrhythmic syncopes with sinus bradycardia and normal QT-interval at rest (author's transl)].

Two children with exercise-induced syncopes are described. There was no evidence for congenital or acquired cardiac defects, cardiomyopathy or myocarditis in either of them. Both had sinus bradycardia and a consistently normal QT-interval at rest. In both, exercise induced regularly a multiform ventricular tachycardia, additionally in one on occasion a bidirectional, in the other a supraventricular tachycardia. Beta receptor blocking agents prevented tachyarrhythmias in both. Under treatment with beta receptor blocking agents, one child remained without syncopes, the other died suddenly. These cases underline the possiblility that exercise-induced syncopes may be caused by tachyarrhythmias even if the QT-interval of the resting Ecg is normal. In suspicious cases an exercise-Ecg is indicated.