Devices, systems, and methods for performing ablation therapy on body tissue are disclosed. An example ablation device for treating body tissue includes an ionically conductive balloon and a radio-frequency electrode that delivers RF energy into a distal section of the balloon. The balloon is configured to transmit the RF energy in a direction distally towards a leading end of the ablation device. Multiple ablation electrodes on the device can be used for providing lesions of different size or shape.