Abstract: An RF ablation system comprises irrigated split tip electrode catheter, an RF generator and a signal processor. The catheter comprises four orthogonally arranged electrodes at the distal tip. The catheter is used to map the electrical activity of a heart chamber to locate site(s) of aberrant electrical pathways to be ablated. Once an ablation site has been located, the signal processor activates the RF generator to transmit a low level RF current to each electrode member of the split tip electrode. The signal processor receives signals indicative of the impedance between each electrode member and one or more surface indifferent electrodes and determines which electrode members are associated with the highest impedance. Such electrode members are those in greatest contact with the myocardium. The signal processor then automatically activates the RF generator to transmit an RF ablation current to the electrode members in contact with the myocardium to create a lesion.