a catheter for facilitating intracardiac atrial defibrillation that includes an elongated flexible member that has a proximal end and a distal end is disclosed . three spaced apart electrode arrays are secured around the periphery of the flexible member in a predetermined pattern so that a first electrode array is positioned within the superior vena cava , a second electrode array is positioned within the right atrium , and a third electrode array is positioned within the coronary sinus . alternatively , the third electrode array may be positioned in the right ventricle rather than the coronary sinus . electrical leads extend through the proximal end of the flexible member to supply electrical current to the electrode arrays , thereby defibrillating or cardioverting the heart .