A method is provided for ablating a portion of the myocardium. The method includes inserting an occlusion catheter into a vessel on a heart, occluding the vessel using the occlusion catheter, inserting an ablation catheter into a chamber of the heart, positioning the ablation catheter against the myocardium, and ablating a portion of the myocardium while the vessel is occluded. The system includes an occlusion catheter having a catheter body including a tubular member having a distal portion and a bend located in the distal portion, a balloon located proximal of the bend and configured to contact an inner surface of the coronary sinus when positioned therewithin, a plurality of marker bands positioned on the catheter body, and a plurality of electrodes positioned on the catheter body.