Abstract: A medical device for ablating tissues within a heart chamber comprising a first guiding member intended to be introduced in the hollow structure surrounding the left atrium of the patient and a second ablating member comprising an ablation electrode mounted at the distal end or tip of catheter. Both, the head of the guiding member and the tip of the ablating member are magnetised and can enter into magnetic coupling when their distal ends are brought in close contact. Once the magnetic coupling is achieved, the tip of the first member is guided by moving the guiding member. Preferably, the guiding member includes sensors enabling to monitor physiological parameters during the intervention.