Implantable medical device with flat aluminum electolytic capacitor

An implantable medical device such as a defibrillator is described. The device includes an hermetically sealed housing containing a flat electrolytic capacitor and an energy source such as a battery. The battery is connected to the capacitor and provides charge thereto. The capacitor stores the charge at a relatively high voltage. The charge stored in the capacitor is discharged through a defibrillation lead to a site on or in the heart when fibrillation of the heart is detected by the implantable medical device. Methods of making and using the implantable medical device, the capacitor, and their various components are disclosed.