An implantable lead adaptor is disclosed that includes an encapsulated thermoplastic housing defining a proximal end portion and a distal end portion. The proximal end portion has a first receptacle configured to receive a first type of connector assembly associated with a first implantable cardiac lead, and a second receptacle configured to receive a second type of connector assembly associated with a second implantable cardiac lead. An elongated flexible lead portion extends from the distal end portion of the adaptor housing. A connector assembly is operatively associated with a distal end section of the flexible lead portion of the adaptor for connection to an implantable pulse-generating device, such as, for example, an implantable pacemaker or defibrillator. Low resistance conductor wires electrically connect the connector assembly associated with the distal end section of the lead portion with the first and second receptacles of the adaptor housing.