Abstract: An implantable cardioverter/defibrillator has an electrode system including two electrodes, at least one of the two electrodes being adapted for placement in a peripheral vein of the heart, the peripheral veins constituting the venous side of the coronary vessels running between the base of the heart and the apex of the heart.

Abstract: An electrode system for a defibrillator avoids the use of a ventricular electrode, and provides efficient utilization of the energy stored in the defibrillator with a beneficial distribution of current in the heart. The electrode system includes three electrodes, at least two of which are intravascular electrodes. One of these intravascular electrodes is placed in the inferior vena cava and the other is placed in the coronary sinus, including its continuation (the great cardiac vein) along the base of the heart. The third electrode can be either an extravascular patch electrode, located in the region of the left ventricle, or an additional intravascular electrode located in the superior vena cava. The intravascular electrodes are devised so that they do not impede the flow of blood in the vein in which they are located.