The company's first model, designated P1, was implanted in three volunteer terminally ill patients in December '64 - January'65, while 2 control samples were retained in a 37 °C. saline bath. This initial design used PNP - NPN electronics to deliver a 2.0 millisecond pulse to the Jeffcoat epicardial electrodes, and was powered by 4 Mallory mercuric oxide-zinc cells (mercury battery), all encapsulated in epoxy resin with a final dip coat of a mix of epoxy and titanium dioxide. All 3 implants failed in ability to maintain capture of the heart after periods of up to 35 weeks. These failures were later proven to be due to the excessively large surface area of the electrodes.