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Figure 5 (Top to bottom) 12-lead surface electrocardiogram, endocardial signals from the right ventricle, and epicardial signals from the left ventricle. The cycle length of the ventricular tachycardia was 510 ms. Pacing from the epicardium shows concealed entrainment and a return cycle identical to the tachycardia cycle length. Ablation was effective at this site.