Abstract: An implantable cardiac defibrillator includes a housing having a thickness dimension that is smaller than either of the length and width dimensions of the housing. Within the housing is an energy storage capacitor having a thickness dimension that is smaller than either of the length and width dimensions of the capacitor. The capacitor includes a first plate layer, a second plate layer, and a dielectric layer separating the first plate layer and the second plate layer. The first plate, second plate and dielectric layers are arranged spirally about an axis parallel to the thickness axis of the capacitor, with the thickness axis of the capacitor being substantially parallel to the thickness axis of the housing. The capacitor is arranged as an annulus having an open center. A battery is disposed within the open center in the same plane as the capacitor. A circuit board and header are arranged in another plane stacked atop the battery and capacitor.