Paul Zoll (1911–1999) invented an electric stimulator device to deliver electrical impulses to the heart externally. In 1958, biomedical engineer Wilson Greatbatch (1919–), in cooperation with doctors William M. Chardack (1915–2006) and Andrew A. Gage (1922–), invented the first internal pacemaker. It was a small, flat, plastic disk powered by a battery. It was implanted into the body and connected by wires sewn directly onto the heart. The wires emitted rhythmic electric impulses to trigger the heart’s action. Pacemaker batteries now last from six to ten years.