A medical device system comprising: a plurality of electrodes positionable in a bodily cavity and a structure on which the electrodes are located, the structure comprising a plurality of elongate members, the plurality of electrodes including a plurality of sets of the electrodes, each respective set of the electrodes located on a respective one of the elongate members, and each of the elongate members comprising a proximal end, a distal end, an intermediate portion positioned between the proximal end and the distal end, and a thickness, each intermediate portion comprising a front surface and a back surface opposite across the thickness of the elongate member from the front surface, wherein the structure is selectively moveable between: a delivery configuration in which the structure is sized for percutaneous delivery to the bodily cavity, and a deployed operational configuration in which the structure is sized too large for percutaneous delivery to the bodily cavity and wherein in the deployed operational configuration: a first elongate member of the plurality of elongate members is positioned such that a portion of the front surface of the first elongate member overlaps a portion of the respective front surface of each of at least a second elongate member of the plurality of elongate members as viewed normally to the portion of the front surface of the first elongate member; at least a first electrode of the plurality of electrodes is located at least on the portion of the front surface of the first elongate member; the portion of the front surface of the second elongate member faces the back surface of the first elongate member; and characterized in that the intermediate portions of the elongate members are angularly arranged with respect to one another about an axis and at least some of the plurality of electrodes are arranged in a plurality of concentric ringed arrangements about said axis, a first one of the plurality of concentric ringed arrangements having a fewer number of the electrodes than a second one of the plurality of concentric ringed arrangements, the first one of the plurality of concentric ringed arrangements comprising the first electrode. a delivery configuration in which the structure is sized for percutaneous delivery to the bodily cavity, and a deployed operational configuration in which the structure is sized too large for percutaneous delivery to the bodily cavity and wherein in the deployed operational configuration: a first elongate member of the plurality of elongate members is positioned such that a portion of the front surface of the first elongate member overlaps a portion of the respective front surface of each of at least a second elongate member of the plurality of elongate members as viewed normally to the portion of the front surface of the first elongate member; at least a first electrode of the plurality of electrodes is located at least on the portion of the front surface of the first elongate member; the portion of the front surface of the second elongate member faces the back surface of the first elongate member; and characterized in that the intermediate portions of the elongate members are angularly arranged with respect to one another about an axis and at least some of the plurality of electrodes are arranged in a plurality of concentric ringed arrangements about said axis, a first one of the plurality of concentric ringed arrangements having a fewer number of the electrodes than a second one of the plurality of concentric ringed arrangements, the first one of the plurality of concentric ringed arrangements comprising the first electrode. a first elongate member of the plurality of elongate members is positioned such that a portion of the front surface of the first elongate member overlaps a portion of the respective front surface of each of at least a second elongate member of the plurality of elongate members as viewed normally to the portion of the front surface of the first elongate member; at least a first electrode of the plurality of electrodes is located at least on the portion of the front surface of the first elongate member; the portion of the front surface of the second elongate member faces the back surface of the first elongate member; and characterized in that the intermediate portions of the elongate members are angularly arranged with respect to one another about an axis and at least some of the plurality of electrodes are arranged in a plurality of concentric ringed arrangements about said axis, a first one of the plurality of concentric ringed arrangements having a fewer number of the electrodes than a second one of the plurality of concentric ringed arrangements, the first one of the plurality of concentric ringed arrangements comprising the first electrode.