A catheter adapted for pulmonary vein isolation, has a distal electrode assembly that can sit stably in an ostium as secured by a plurality of spines and a membrane member. Preshapened and flexible, the spines support the membrane in a concave configuration when the distal electrode assembly approaches the ostium, the spines and membrane member being sized and configured to span across and over the ostium. As the distal electrode assembly is pushed into the ostium, the membrane member elastically deforms, generally turning inside out to expose surface electrodes carried on a contact surface of the membrane member and ring electrodes carried on the spine for contact with the ostium. The membrane member may be inflated. The ring electrodes contact tissue along axial lines of the ostium. The surface electrodes contact tissue along radial lines of the ostium.
