The technique of endocardial mapping was developed by the advancement of radiofrequency catheter ablation techniques. Because the catheter ablation has been performed various complex arrhythmias, simple-catheter based mapping methods was limited and multiple electrodes catheter mapping and computed mapping system were developed. The basket catheter has 64-unipolar electrodes and can records endocardial potential during arrhythmia for a moment. The electro-anatomical mapping system, CARTO system, can records entire circuit of arrhythmia and point the critical area, but it will expend more time for mapping and can not indicate for unstable arrhythmias. The new mapping systems, include noncontact mapping system and LocaLisa system, will be able to use in the near future in Japan.