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Figure 4 Top: Electrogram of the onset of ventricular fibrillation 21 min after occlusion. The shaded area (diagram) designates ischemic tissue; the pulse shows the site of stimulation. Dots in the enlarged multi-electrode represent electrode positions; the circle represents the site of focal origin. The dotted line indicates the electrophysiological border. A, B and C are activation maps of the corresponding beats. Lines indicate 5 ms isochrones; arrows indicate gross activation sequence; numbers indicate times relative to the last stimulus artefact; the asterisk indicates the site of origin. Note the absence of R wave in local electrogram recorded from the site of origin (top).