Kieny JR, Roul G, Sachs D, Mossard JM, Bareiss P, Sacrez A/ CHU Hautepierre, Strasbourg. Arch Mal Coeur Vaiss 1991, 84(11):1587-90. The utility of transesophageal atrial pacing in sustained left ventricular tachycardia is reported in two cases. A 46 year old man without any apparent cardiac disease presented with invalidating but undocumented palpitations. Transesophageal atrial pacing with isoproterenol infusion induced wide complex tachycardia with a right bundle branch block morphology and left axis deviation. Atrio-ventricular dissociation was observed and it was possible to reduce the ventricular complex width by rapid transesophageal atrial pacing: the tachycardia was terminated by an injection of verapamil. It was not possible to reinduce the tachycardia after treatment with atenolol 100 mg/day, introduced because of the catecholinergic nature of the arrhythmia. The patient is symptom free after 2 years of treatment with this drug. Regular wide complex tachycardia with right bundle branch block and left axis deviation without any detectable atrial activity was recorded in a 50 year old man without known cardiac disease. Transesophageal atrial pacing with isoproterenol infusion induced an identical tachycardia. The tachycardia started after a normally conducted atrial extrastimulus followed by ventriculo-atrial dissociation and it was possible to overdrive with atrial pacing. The tachycardia could not be reinduced after treatment with atenolol and the patient is asymptomatic 12 months later. These reports show that it is possible to study certain ventricular tachycardias by transesophageal atrial pacing. The efficacy of antiarrhythmic therapy can be controlled simply by this non-invasive technique.