Tissue heating and ablation systems and methods use a porous electrode assembly with an electrically conductive surface. The electrode assembly includes an exterior peripherally surrounding an interior area. At least a portion of the wall comprises an electrically conductive material. A lumen conveys a medium containing ions into the interior area. According to the invention, at least a portion of the wall also comprising a porous material sized to pass ions contained in the medium. In a preferred embodiment, the electrode assembly further includes an element coupling the electrically conductive material to a source of electrical energy to transmit electrical energy. In this preferred embodiment, the electrically conductive material is also porous to pass ions contained in the medium. The assembly also preferably includes a conductive element coupling the medium within the interior area to a source of electrical energy to enable ionic transport of electrical energy by the medium through the porous material.