An implantable heart stimulator has an electrically conductive housing containing a pulse generator, with an electrode lead connected to the housing. The electrode lead has a proximal portion extending substantially from the housing to a location, after implantation, which is beyond the entry of the lead into the venous system and before the entry of the lead into the superior vena cava. A current source supplies an infection control current between the housing and an electrically conductive surface on the exterior of the proximal portion of the electrode lead, for counteracting bacterial growth. The housing may have a header to which the electrode lead is connected, in which case the header is provided with an electrically conductive surface as well, which can serve as an electrode for the infection control current.