An 80-year-old is presenting woman with ischemic cardiomyopathy and advanced heart failure (New York Hear Association class III), despite optimal medical therapy. Left ventricular ejection fraction is 27%.

• Sinus rhythm, 60/min
• Left bundle branch block – QRS duration 180 msec.

The patient was referred to the Electrophysiology (EP) service and a therapeutic procedure was carried out:

• VVI pacing, 60/min
• Underlying atrial fibrillation
• Right superior QRS axis (250 °)
• ECG findings suggestive of biventricular pacing

Comments: The patient had undergone implantation of a biventricular pacemaker for Cardiac-Resynchronization Therapy (CRT). The atrial lead was positioned in the right atrial appendage, the right ventricular lead in the RV apex and the left ventricular lead in lateral coronary vein branch. The presence of a Q wave in lead I and R wave in Lead V1 suggest left to right activation in the ventricle and are diagnostic for LV pacing.