A system for forming a fistula comprising: a first catheter configured to be advanced through a first vessel, the first catheter comprising one or more first catheter magnetic elements and a fistula-forming element ; a second catheter configured to be advanced through a second vessel, the second catheter comprising one or more second catheter magnetic elements , wherein the one or more first catheter magnetic elements and the one or more second catheter magnetic elements are configured to draw the first catheter and the second catheter together; characterised in that the system further comprises one or more magnetic field sensors configured to output a magnetic field signal indicative of a magnitude of a magnetic field produced between the one or more first catheter magnetic elements and the one or more second catheter magnetic elements; a user output device configured to output a ready signal; and a controller communicatively coupled to the one or more magnetic field sensors and the user output device, wherein the controller is configured to: receive the magnetic field signal from the one or more magnetic field sensors; determine a distance of separation of the first catheter from the second catheter based on the magnetic field signal from the one or more magnetic field sensors; and output the ready signal with the user output device in response to determining that the distance of separation of the first catheter from the second catheter is a predetermined distance or less, wherein the ready signal is indicative of proper alignment and position of the first catheter and the second catheter to form the fistula with the fistula-forming element. a first catheter configured to be advanced through a first vessel, the first catheter comprising one or more first catheter magnetic elements and a fistula-forming element ; a second catheter configured to be advanced through a second vessel, the second catheter comprising one or more second catheter magnetic elements , wherein the one or more first catheter magnetic elements and the one or more second catheter magnetic elements are configured to draw the first catheter and the second catheter together; characterised in that the system further comprises one or more magnetic field sensors configured to output a magnetic field signal indicative of a magnitude of a magnetic field produced between the one or more first catheter magnetic elements and the one or more second catheter magnetic elements; a user output device configured to output a ready signal; and a controller communicatively coupled to the one or more magnetic field sensors and the user output device, wherein the controller is configured to: receive the magnetic field signal from the one or more magnetic field sensors; determine a distance of separation of the first catheter from the second catheter based on the magnetic field signal from the one or more magnetic field sensors; and output the ready signal with the user output device in response to determining that the distance of separation of the first catheter from the second catheter is a predetermined distance or less, wherein the ready signal is indicative of proper alignment and position of the first catheter and the second catheter to form the fistula with the fistula-forming element. receive the magnetic field signal from the one or more magnetic field sensors; determine a distance of separation of the first catheter from the second catheter based on the magnetic field signal from the one or more magnetic field sensors; and output the ready signal with the user output device in response to determining that the distance of separation of the first catheter from the second catheter is a predetermined distance or less, wherein the ready signal is indicative of proper alignment and position of the first catheter and the second catheter to form the fistula with the fistula-forming element. <EOS>