The present invention relates to a probe assembly for mapping and ablating pulmonary vein tissue and method of using the same. The probe assembly includes an expandable and collapsible basket assembly having multiple splines. One or more of the splines carry one or more electrodes adapted to sense electrical activity in the pulmonary vein tissue. The basket assembly defines an interior, and a microporous expandable and collapsible body is disposed in the interior of the basket assembly and defines an interior adapted to receive a medium containing ions. An internal electrode is disposed within the interior of the body and is adapted to transmit electrical energy to the medium containing ions. The body includes at least one microporous region having a plurality of micropores therein sized to pass ions contained in the medium without substantial medium perfusion therethrough, enabling ionic transport of electrical energy from the internal electrode, through ion-containing medium to an exterior of the body to ablate pulmonary vein tissue. In other aspects of the invention, the microporous body may be replaced by a non-porous expandable and collapsible body that receives a fluid medium for expanding the non-porous body to exclude blood from the electrodes on the splines, or the probe assembly may not include any expandable and collapsible body in the basket assembly interior (one or more electrodes on splines sense electrical activity in the pulmonary vein tissue and ablate the pulmonary vein tissue).