Medical apparatus, comprising: a sheath, adapted for insertion into a body of a patient and having a lumen with a distal opening; a flexible probe, which is adapted for insertion through the sheath and comprises: an insertion shaft, having a distal end; an end section, which is connected to the distal end of the insertion shaft and comprises a distal tip; a tip electrode extending over the tip; a plurality of proximal electrodes distributed along the end section; and a position transducer configured to provide a signal, wherein the probe is manipulable, within the sheath, between a retracted configuration in which the end section is contained within the lumen so that only the tip electrode protrudes through the distal opening, and an extended configuration in which the entire end section protrudes from the distal opening and assumes an arcuate shape; and an energy generator, and characterised in that: the sheath comprises a positioning element in proximity to the distal opening; the energy generator is configured to apply electrical energy only to the tip electrode while the probe is in the retracted configuration and to apply the electrical energy to at least the proximal electrodes while the probe is in the extended configuration, and the energy generator is configured to apply the electrical energy only to the tip electrode when the signal provided by the transducer indicates that the transducer is within a predetermined minimum distance of the positioning element. a sheath, adapted for insertion into a body of a patient and having a lumen with a distal opening; a flexible probe, which is adapted for insertion through the sheath and comprises: an insertion shaft, having a distal end; an end section, which is connected to the distal end of the insertion shaft and comprises a distal tip; a tip electrode extending over the tip; a plurality of proximal electrodes distributed along the end section; and a position transducer configured to provide a signal, an insertion shaft, having a distal end; an end section, which is connected to the distal end of the insertion shaft and comprises a distal tip; a tip electrode extending over the tip; a plurality of proximal electrodes distributed along the end section; and a position transducer configured to provide a signal, wherein the probe is manipulable, within the sheath, between a retracted configuration in which the end section is contained within the lumen so that only the tip electrode protrudes through the distal opening, and an extended configuration in which the entire end section protrudes from the distal opening and assumes an arcuate shape; and an energy generator, and characterised in that: the sheath comprises a positioning element in proximity to the distal opening; the energy generator is configured to apply electrical energy only to the tip electrode while the probe is in the retracted configuration and to apply the electrical energy to at least the proximal electrodes while the probe is in the extended configuration, and the energy generator is configured to apply the electrical energy only to the tip electrode when the signal provided by the transducer indicates that the transducer is within a predetermined minimum distance of the positioning element.