The invention relates to an ablation catheter which controls the temperature and reduces the coagulation of biological fluids on an electrode of a catheter, prevents the impedance rise of tissue in contact with the electrode, and maximizes the potential energy transfer to the tissue, thereby allowing an increase in the lesion size produced by the ablation. The electrode includes passages positioned to allow saline flow out of an inner cavity of the electrode. This fluid flow produces the desired cooling effect and is accomplished, for example, by saline irrigation flow with a valve element to block flow of blood into the inner cavity of the electrode.