A system for cardiac treatment, comprising: a catheter configured for insertion into a chamber of a heart of a patient; and a processor, which is configured to receive an initial map of a chamber of a heart of a patient, acquired in an initial ablation procedure, with locations of ablation lesions marked on the initial map, characterised in that said processor is coupled to acquire a current map of the chamber using the catheter in preparation for a redo ablation procedure, subsequent to the initial ablation procedure, and to register the initial map with the current map and to mark and display on the current map the locations of the ablation lesions from the registered initial map; wherein the processor is configured to register the initial map by identifying at least one anatomical landmark in both the initial map and the current map, and aligning the at least one landmark identified in the initial map with a position of the at least one landmark identified in the current map; wherein the chamber is a left atrium of the heart, and the at least one landmark comprises a carina between superior and inferior pulmonary veins connecting to the left atrium; wherein the processor is configured to superimpose on the current map wide circumferential ablation lines produced in the initial ablation procedure, and wherein the redo ablation procedure comprises ablating further tissue in the chamber at sites chosen to close at least one conduction gap in the WCA; wherein the catheter is configured to sense electrical activity in the chamber of the heart, and the processor is configured to display an indication of the sensed electrical activity on the current map, showing a conduction gap between the ablation lesions; and wherein the redo ablation procedure comprises ablating further tissue in the chamber, and wherein the processor is configured to mark and display on the current map the locations of further ablation lesions created by ablating the further tissue together with the ablation lesions from the registered initial map. a catheter configured for insertion into a chamber of a heart of a patient; and a processor, which is configured to receive an initial map of a chamber of a heart of a patient, acquired in an initial ablation procedure, with locations of ablation lesions marked on the initial map, characterised in that said processor is coupled to acquire a current map of the chamber using the catheter in preparation for a redo ablation procedure, subsequent to the initial ablation procedure, and to register the initial map with the current map and to mark and display on the current map the locations of the ablation lesions from the registered initial map; wherein the processor is configured to register the initial map by identifying at least one anatomical landmark in both the initial map and the current map, and aligning the at least one landmark identified in the initial map with a position of the at least one landmark identified in the current map; wherein the chamber is a left atrium of the heart, and the at least one landmark comprises a carina between superior and inferior pulmonary veins connecting to the left atrium; wherein the processor is configured to superimpose on the current map wide circumferential ablation lines produced in the initial ablation procedure, and wherein the redo ablation procedure comprises ablating further tissue in the chamber at sites chosen to close at least one conduction gap in the WCA; wherein the catheter is configured to sense electrical activity in the chamber of the heart, and the processor is configured to display an indication of the sensed electrical activity on the current map, showing a conduction gap between the ablation lesions; and wherein the redo ablation procedure comprises ablating further tissue in the chamber, and wherein the processor is configured to mark and display on the current map the locations of further ablation lesions created by ablating the further tissue together with the ablation lesions from the registered initial map.