Method and apparatus for treating conductive irregularities in the heart, particularly atrial fibrillation and accessory path arrythmias. An ablative catheter is positioned relative to an inter-atrial electrical pathway, or a vicinity of accessory paths such as the coronary sinus or fossa ovalis, and actuated to form a lesion that partially or completely blocks electrical conduction in at least one direction along the pathway. Method and apparatus for assessing lesion quality are also described.
