implantable defibrillators are implanted into the chests of patients prone to suffering ventricular fibrillation , a potentially fatal heart condition . a critical component in these devices is an aluminum electrolytic capacitors , which stores and delivers one or more life - saving bursts of electric charge to a fibrillating heart . these capacitors make up about one third the total size of the defibrillators . unfortunately , conventional manufacturers of these capacitors have paid little or no attention to reducing the size of these capacitors through improved capacitor packaging . accordingly , the inventors contravened several conventional manufacturing principles and practices to devise unique space - saving packaging that allows dramatic size reduction . one embodiment of the invention uses thinner and narrower separators and top and bottom insulative inserts to achieve a 330 - volt operating , 390 - volt surge , 190 - microfarad , 30 - joule aluminum electrolytic capacitor which is 33 percent smaller than conventional capacitors having similar electrical traits .