The present invention provides an irrigated ablation electrode that includes a plurality of high L/d interior fluid passageways and/or slit-shaped apertures to provide for a lower rate of fluid flow and a more uniform distribution of fluid over an exterior surface of the electrode and reduce propensity for aperture blockage. In some embodiments, the slit-shaped apertures have an aspect ratio of at least three, at least five, at least ten, or at least fifteen. Some embodiments include maintaining a pressure drop of at least 345 pascals between irrigation fluid inside the irrigated ablation electrode and fluid immediately outside the electrode when the irrigation fluid has a flow rate of no more than five milliliters per minute (5 ml/min). Some embodiments include a low-density insert with a plurality of fluid channels on its exterior surface to more efficiently cool the electrode and provide a faster thermal response.
