Abstract: An implantable assembly for defibrillation and monitoring and/or regulating the beat of a heart. The defibrillation electrode is flexible and preferably made of braided carbon fiber and conductive metallic wire. It provides a low polarization, low capacitance and low impedance electrical interface with body fluid and/or excitable tissue. The conductivity of the defibrillation electrode is increased over electrodes made only of carbon fiber by the presence of the conductive metallic wire in the preferred embodiment, or by a thin exterior coating of titanium and silver in another embodiment. This electrode delivers energy more efficiently to body tissue than conventional defibrillation electrodes, resulting in lower energy needed to achieve defibrillation, which allows batteries powering the defibrillator to last longer.