The first fully implantable cardiac pacemaker was developed by Rune Elmqvist and surgeon Åke Senning in Sweden in 1958. A pacemaker is a small device that sends electrical pulses to the heart to help it beat at a normal rate and rhythm. Early external versions were bulky and had to be plugged into a wall, making them dangerous during power outages. Wilson Greatbatch, an American engineer, later invented a much more reliable version using a lithium battery that could last for years. This invention has transformed the treatment of heart block and arrhythmia, allowing millions of people with cardiac conditions to live long, active lives. It represents a landmark in the field of bioengineering, where electronic devices are integrated directly into the human body to manage vital biological functions.