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PM-65 by Paul Zoll allowed the patient to ambulate (1955) [Reproduced with permission of The Bakken Library and Museum of electricity in Life, MN, USA]
“We would put terrible, frightful electrodes on. They would stimulate all of the chest muscles and were kind of painful. But people who would otherwise have died were brought along. That was kind of miraculous.”
see http://www.machine-history.com/Cardiac%20Pacemaker