In order in the case of a catheter for the ablation of biological, in particular of animal or human, tissue, preferably for the ablation of human myocardial tissue, having at least one ablation or mapping electrode to permit the recording of ECG signals during catheter ablation and, in particular, to improve the quality of the recorded ECG signals to such an extent as to permit medical statements with reference to cardiac action, it is provided that the at least one ablation or mapping electrode has a reduced number of electrical interference centres. Furthermore, the invention provides methods and apparatuses with the aid of which conventional catheters can be treated in such a way that these interference centres are reduced.