A system for performing a medical intervention in a subjects body comprises a medical device (10) comprising several segments (12, 15) to be navigated through the body lumens, an external magnet and a control unit connected with the magnet adapted to generate control signals for the external magnet to generate a magnetic field (B) having a direction (40) to orient a magnetically responsive element (25) in the distal end portion (20) of the medical device (10), especially to cause the distal end portion (20) of the medical device (10) to bend in a given direction (30) for improving navigation. The control unit is configured to store the current direction of the distal end portion (30) or the current direction of the magnetic field (B) as stored direction and to subsequently limit the generation of control signals for the external magnet(s) in a way that the direction of the magnetic field (B) is limited within a field limiting frame (60) around the previously stored direction.
