A catheter adapted for pulmonary vein isolation, has a distal electrodeassembly that cansit stably in an ostium as secured by a plurality of spines and a membranemember.Preshapened and flexible, the spines support the membrane in a concaveconfiguration whenthe distal electrode assembly approaches the ostium, the spines and membranemember beingsized and configured to span across and over the ostium. As the distalelectrode assembly ispushed into the ostium, the membrane member elastically deforms, generallyturning inside outto expose surface electrodes carried on a contact surface of the membranemember and ringelectrodes carried on the spine for contact with the ostium. The membranemember may beinflated. The ring electrodes contact tissue along axial lines of the ostium.The surfaceelectrodes contact tissue along radial lines of the ostium.
