An ablation device, including a catheter and an ablation element incorporating one or more balloons at the distal end of the catheter, has a continuous passageway extending through it from the proximal end of the catheter to the distal side of the expandable ablation element. The ablation device ablates tissue by subjecting it to ultrasound energy, cryogenic energy, chemical, laser beam, microwave, or radiation energy. A probe carrying electrodes is introduced through this passageway and deploys, under the influence of its own resilience, to a structure incorporating a loop which is automatically aligned with the axis of the expandable ablation device, so that minimal manipulation is required to place the probe. Pulmonary vein potential is monitored in real time via the electrodes. The probe may have an atraumatic tip with a ball formed at the leading edge. The atraumatic tip prevents any tissue damage such as perforation of heart wall.