Described embodiments include an apparatus, including a display and a processor. The processor is configured to navigate a catheter to a particular location within a body of a subject, using each one of a plurality of electrodes coupled to the body of the subject. The processor is further configured to identify, subsequently, from a signal that represents an impedance between a given pair of the electrodes, that a phrenic nerve of the subject was stimulated by a pacing current passed from the catheter into tissue of the subject at the particular location, and to generate an output on the display, in response to the identifying. Other embodiments are also described.