Triggered activity was shown to be the likely mechanism of recurrent tachycardia in a 28 year old Vietnamese man. During baseline electrophysiological testing the tachycardia was induced consistently by prolonged atrial or ventricular pacing but not by premature extrastimuli. Moreover, the tachycardia coupling intervals varied directly with the cycle length of the initiating drive. Procainamide and propranolol did not suppress tachycardia, but verapamil terminated it and prevented its reinitiation. The origin of the tachycardia was localised to the left ventricular inferoapical segment and four direct current countershocks of 200 J each delivered via an electrode catheter abolished the tachycardia. During 12 months of follow up the patient was not treated with antiarrhythmic agents and the tachycardia did not recur.