Abstract: A device for locating an electrode used in endocardial treatment comprises further electrode means to be positioned inside the heart together with the electrode, the further electrode means being able to adopt a geometrical arrangement defining a system of spatial coordinates. Polarization means are provided for applying respective electrical signals to at least one of the electrode and the further electrode means, as well as detector means connected to the electrode and to the further electrode means for detecting the potential established between the electrode and the further electrode means as a result of the application of the electrical signals. Measuring means sensitive to the potential are capable of determining, on the basis of the potential, the position of the electrode relative to the system of spatial coordinates defined by the further electrode means.