Verapamil-sensitive but adenosine resistant left ventricular tachycardia (fascicular tachycardia) is a recognised cause of ventricular tachycardia occurring in patients without overt cardiac disease. This study addresses (1) the efficacy of radiofrequency ablation guided by pace-mapping technique in the treatment of this tachycardia, and (2) the location of this tachycardia in the left ventricle as assessed by simultaneous ventriculography. Five patients (two women and three men, mean age 25 +/- 8 years) with ventricular tachycardia exhibiting a right bundle branch block and left axis deviation morphology, with documented response to verapamil but resistance to intravenous adenosine triphosphate were studied. Biplane left ventricular cineangiography was first performed to visualise the topography of the left ventricle. Pace-mapping at a rate within 10 beats/min of the tachycardia rate was performed, and the concordance of paced QRS configuration with that of the induced tachycardia was compared for each of the 12 leads for major or minor differences. A perfect pace-map could be achieved in all five patients (two in posteroseptal left ventricle and three in the posterior left ventricular wall). Five of eight applications at an identical pace-map resulted in suppression of tachycardia induction, whereas none of the 39 applications at sites with a less identical map was successful (P < 0.001). After a successful procedure, there was no recurrence as assessed clinically, by non-invasive monitoring (event recording, Holter monitoring and exercise testing for all patients) and repeat electrophysiology testing (three patients) during a follow-up of 12 +/- 3 months. Thus radiofrequency ablation guided by pace-mapping technique is a highly efficacious treatment for fascicular tachycardia. The response to radiofrequency ablation suggests the origin of tachycardia as reentry circuits involving the lower septum or posterior part of the left ventricle close to or within the endocardial surface.