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Discontinuous linear ablation lesions can be a cause of proarrhythmias such as re-entrant tachycardias. Assessment of the wall contact and prevention of proarrhythmic gaps remain crucial. The technique of direct visualisation of the discontinuities between ablation lesions is not well established. Intracardiac echocardiography (ICE) is a technique that can be used to visualise various intracardiac structures that are not visualised on fluoroscopy and which allows precise localisation of intracardiac catheters relative to these anatomical structures. A deflectable 8.5 MHz phased array ICE catheter (Acu Nav, Acuson Inc) detected a real time histological gap on the posterior wall of the left ventricle in vivo in a canine model (below left, arrowhead). Low power energy deliveries were made in the left ventricle for 60 seconds. The target temperature was 60° with a maximum power of 40 W, which was the same as that used in the clinical setting. The ablation lesions were vividly demonstrated by the presence of an increase in the tissue density. The gap between the two ablation lesions was detected as a relatively hypoechoic area. The real time measurement of the maximum distance between the two lesions was 3.1 mm. A histological examination revealed sharply demarcated ablation lesions and a histological gap (below right). Macroscopically, the maximum size of the gap measurement was 3 mm. The size of the gap in ICE may be useful in the direct identification of discontinuation lesions in linear low power ablation.