Report of attacks of ventricular tachycardia in a 39 year-old man, free from heart disease. Cardiac pacing showed that the tachycardia could be induced by premature supraventricular beats normally propagated to the ventricles, and by atrial acceleration. The same part played by the cardiac rate on triggering of attacks was demonstrated during ventricular pacing. Besides, the possibility to interrupt the tachycardia by one electrically induced ventricular beat, supports the hypothesis of a re-entry machanism. The QRS configuration during the arrythmia suggested a propagation of excitation starting from the posterior-inferior area of the left ventricle. However, the absence of anomalies of the supraventricular beats initiating the tachycardia excluded a circus movement resulting from a unidirectional block on the left anterior hemibranch. More probably there existed an area of micro-reentry, stimulating the left ventricle from the posterior branches of the His-Purkinje system.