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Aims Conduction through separated myocyte bundles causes multipotential electrograms and reentrant ventricu-lar tachycardia. We hypothesized that without initiating tachycardia, the reentry region could be detected by ana-electrograms were present during one activation sequence (20%). Multipotential electrograms with>2 low amplitude deflections and a>100 ms difference in duration between the two activation sequences were infrequent but highlyIntroduction Sustained monomorphic ventricular tachycardia late af-ter myocardial infarction is usually due to reentry in the border zone of the infarct. The reentry circuit paths and isthmuses are defined by regions of conduction block. Block may be fixed, due to areas of fibrosis, or func-tional and present only during reentry due to incomplete recovery from depolarization or to collision of wavefronts[1–3]. Most circuits contain a relatively narrow isthmus in the infarct. Radiofrequency catheter ablation aims to interrupt the tachycardia at these narrow isth-mus sites, which are a critical part of the circuit. Precise identification of these isthmuses may be impossible, however, when ventricular tachycardia is unstable for mapping due to haemodynamic instability during tachy-cardia, poor reproducibility of initiation, or frequent transformation from one tachycardia to another. Iden-tification of markers for ventricular tachycardia isth-muses that do not require mapping during tachycardia is desirable, but using analysis of sinus rhythm electro-grams for this purpose has been discouraging. Abnormal sinus rhythm electrograms are present over broad regions of the infarct that include reentry circuit sites, but also include bystander regions that are not in the circuit[4–6]