Abstract: An ablation electrode is mounted on the distal end of a catheter with a first portion inside and a second portion outside the catheter. The second portion is adapted to have a surface that makes maximum contact with a tissue to be ablated, leaving a minimum area not covered by the tissue and potentially exposed to blood. The first portion is adapted to provide an extended surface area for efficient exchange of heat with a coolant flowing inside the catheter. Outlets provided near the area not covered by the tissue in the second portion prevents blood from getting close to or come directly in contact with the area, thereby greatly reducing formation of dangerous blood clots. The minimizing of an electrical circuit through blood greatly reduces wasted power into the electrode so that the efficiently cooled electrode is not burdened. The catheter preferably has multiple electrodes with similar features.