Abstract
This is a report of a case of bidirectional tachycardia in a 6-year-old girl with no evidence of any structural abnormality of the heart. The patient had never received digitalis. The arrhythmia appeared to be precipitated by effort and emotional stress, and could be induced by increasing the heart rate by atrial pacing or isoprenaline administration. His bundle electrography showed that the arrhythmia was ventricular in origin. This emphasizes the importance of recording an effort electrocardiogram in all children with unexplained syncopal episodes, even when the resting electrocardiogram is normal.