There are 2 things that you could be asking,who found the anatomical pacemaker, the area of the heart that controls it's rate, this was identfied in 1907 by Arthur Keith and Martin Flack.
Alternatively you may be asking who designed the first artificial pacemaker
. The first external pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950. The first implantation
into a human was made in 1958 by a Swedish team using a pacemaker designed by Rune Elmqvist and Åke Senning. The device failed after three hours.