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A 58-year-old man with hypertension and half a year ago documented left bundle branch block (LBBB) in his past history presented with progressive dyspnea.A pre-admission echocardiography showed severely depressed systolic left ventricular function [ejection fraction (EF) =27％], diffuse hypokinesis and dilated heart chambers consistent with dilated cardiomyopathy (DCM).On admission, he presented with dyspnea on minimal exertion, his blood pressure was 100/70 mmHg, his heart rate was 62 beats/min with occasional mild irregularities suggesting premature beats.The electrocardiogram (ECG) showed a 67 beats/min sinus rhythm with complete LBBB pattern and a QRS duration of 170 ms (Figure 1A).Telemetry first revealed a 170-175 beats/min wide QRS complex tachycardia (WCT) consisting of six beats with right bundle branch block (RBBB) pattern, which followed a 62 beats/min sinus rhythm with LBBB pattern (Figure 1B), later showed two initial sinus beats with a heart rate of 54 beats/min and LBBB pattern and a QRS duration of 170 ms followed by an irregular wide QRS complex rhythm with a 78-102 beats/min mean ventricular rate, with QRS complexes of 150 ms QRS duration and a QRS morphology resembling LBBB (Figure 1C).Apparently at first glance, AV dissociation was not present during the irregular wide QRS complex rhythm, because the number of P-waves and QRS complexes were equal.