A 43-year-old man with episodes of rapid palpitation occurring every few weeks, often caused by exercise and accompanied by dyspnea and weakness that usually subsides spontaneously after 15-20 minutes is presenting to the emergency department one hour after onset of a typical episode:

• Wide QRS tachycardia, most likely ventricular tachycardia, 160/min 
• QRS duration 152 ms 
• Right bundle branch block pattern with monophasic R wave in V1 and right superior axis deviation

The patient was administered IV adenosine, with termination of arrhythmia:

• Ventricular tachycardia, 164/min followed by restoration of sinus rhythm arrhythmia, 57/min

The following ECG is recorded shortly after restoration of sinus rhythm:

• Sinus rhythm, 80/min
• Shifting of the baseline in the left chest leads makes the assessment of the ST segment questionable 
• Probably normal ECG

Comments: A thorough investigation showed no evidence of structural heart disease. During EP studies ventricular tachycardia with the same pattern as in ECG 1 was induced by isoproterenol infusion. The VT was identified as a reentrant circuit within the left posterior fascicle and was successfully ablated. At the end of the procedure VT could no longer be induced with isoproterenol infusion.