A thin, elongate and flexible ablation catheter, suitable for delivery to an internal organ, comprises a fluid delivery lumen centrally located within the catheter, and first and second electrodes disposed on an outer surface of the catheter. The electrodes preferably are helically oriented about the catheter. At least one of the electrodes is in communication with a source of electrosurgical energy so as to deliver ablative electrosurgical energy to tissue. The lumen communicates with a fluid supply source such that fluid is conveyed through the lumen and is discharged to adjacent tissue during the delivery of ablative energy. The fluid delivered through the lumen assists in optimizing the electrode temperature. A method and apparatus is also provided to regulate the fluid flow rate based on monitored electrode temperature and/or tissue impedance.