A removable apparatus is provided for temporary implantation in a pulmonary vein for ablating atrial tissue surrounding the antrum of the pulmonary vein to treat atrial fibrillation in a subject. The apparatus comprises an electrically-insulated expandable support member and a retrieval mechanism. The support member has oppositely disposed proximal and distal end portions and a main body portion extending between the end portions. The proximal end portion includes at least one annularly disposed wing member, and has a free end defined by oppositely disposed first and second major surfaces. The at least one wing member includes at least one ablation element located at the free end thereof. The retrieval mechanism is for removing the support member and for energizing the at least one ablation element. The retrieval mechanism includes at least one electrically-conductive wire, which is separately connected to the at least one wing member.