Abstract: An electrode member insertable from without through the epicardium into the heart muscle, as part of an implantable pacemaker, comprises a holder of dielectric elastic material including a tubular stem terminating in an enlarged resilient pad having the shape of a platform. One major surface of the platform pivotally supports a metallic hook which is swivelable about an axis perpendicular to that surface and is electrically connected to a conductor extending within the stem to a generator of electric pulses. Upon insertion of the hook from the outside through the epicardium into the heart muscle by a tool gripping that hook, release of the hook allows the elastic pad to expand against the outer heart surface to anchor the electrode member in position.