Abstract: Implantable electrode structures for use in apparatus for applying electrical therapy to a patient's heart in the treatment of arrhythmias such as tachycardias and fibrillations of the heart are herein disclosed. The electrode structures are made in the form of expandable (or self-expanding) intravascular stents for insertion through the patient's vascular system to locations in or adjacent the heart. The electrode structures can be inserted into the great veins by insertion techniques used for intravascular stent applications and provide increased electrode surfaces for discharge of electrical energy through the heart in conjunction with other strategically placed electrodes. The wire filament of the stents may be evenly spaced to form a circumferential array or may be non-uniformly spaced to form an elliptical array.