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Figure 4 Cisapride (0.2 µmol/l) permits induction of torsades de pointes during epicardial (Epi) but not endocardial stimulation. Epicardial and M-cell action potentials and a transmural electrocardiogram were simultaneously recorded during endocardial (A) and epicardial (B) pacing of the canine left ventricular wedge preparation at a basic cycle length of 2,000 ms. A polymorphic ventricular tachycardia was induced by an extrastimulus delivered to epicardium at an S1-S2 interval of 204 ms (C). ECG = electrocardiogram; other abbreviations as in Figure 2. Modified and reprinted, with permission, from Fish et al. (5).