Embodiments of the present invention are directed to ablation catheter systems configured, for example, to ablate tissue adjacent an ostium of the pulmonary vein in a left atria of a heart. In one embodiment, an ablation catheter system includes a handle and a catheter coupled to the handle defining a lumen extending through a length of the catheter, the catheter including a distal end thereof. The ablation catheter system may also include an electrode coupled to the handle with lines extending through the lumen of the catheter, the electrode being configured to be constrained adjacent the distal end of the catheter and configured to be deployed from the distal end of the catheter to an expanded configuration.