A cardiac ablation catheter (100) includes a coil-like ablating element (102) that is deployed from an elongate, flexible sheath (104). The ablating element (102), while in the deployed position, has a shape with at least one revolution oriented in a plane that is orthogonal to a longitudinal axis (108) of the sheath. The catheter system (100) is well-suited to ablate a circumferential region of tissue about a pulmonary vein or the posterior wall of the left atrium proximate the pulmonary vein os. The treated tissue region electrically isolates the atria from the pulmonary vein.