A method for assessing a lesion formed between first and second regions of body cavity tissue, the method including using a first probe in contact with the tissue at a stimulus location in the first region, and applying to the tissue or sensing in the tissue a first activation signal having a first activation peak at a first time. Respective second activation signals having respective second activation peaks following the first activation signal are received from a second probe having multiple electrodes in contact with the tissue at respective sensing locations in the second region, and based on a temporal relation between the first and second activation peaks and a spatial relation between the stimulus location and the sensing locations, one of the multiple electrodes proximal to a gap in the lesion is identified. A map of the body cavity is displayed with the identified electrode marked on the map.