A liquid leak stop for an implantable heart pacer. There is disclosed an implantable heart pacer for providing stimulation to the heart of a patient. The pacer includes a heartbeat detector, a pulse generator, batteries for powering or energizing the electronics, and electrodes or terminals for connection to the heart. Human body fluids tend to leak into the electrode throat or connector receptacle of the implantable pacer. This leakage can cause pacer malfunction. There are disclosed means for halting this leakage along conductors connecting the pacerexternal electrodes and the pacer-internal electronics.