AbstractThe isotopic cardiac pacemaker directly applies nuclear technology to the field of medicine. Developed in 1970, the Laurens-Alcatel Model 9000 Pacemaker is now being implanted in humans in strict accordance with procedures set down by various regulatory agencies. This paper is an interim report on the reliability tests (with the resultant data) that have been performed on the isotopic cardiac pacemaker.The theoretical data for the longevity of the isotopic generator are discussed, as are the results for resistance to shock and corrosion tests. Comparative data are also given on the energy density of the isotopic generator and compared with other electrical power sources commonly used in cardiac pacing. The source thermal 238Pu source has also been subjected to increasingly severe tests to ensure complete containment of all radioactive material.