A system for ablating bodily tissue of a patient includes a high-voltage electrical generator configured to provide electrical pulses of at least 500 volts, a fluid having an electrical conductivity of not more than 0.01 Siemens per meter, and an ablation catheter that includes a catheter shaft, an expandable membrane attached to the catheter shaft, and a plurality of electrodes, each electrically coupled to the high-voltage electrical generator. The fluid inflates the expandable membrane when provided to the interior space of the expandable membrane.