Electrocardiographs measure the small electrical currents generated by beating hearts. Willem Einthoven, a Dutch physiologist, invented an electrocardiograph—which he termed a string galvanometer—in 1901. The first electrocardiograph in the United States was the commercial model that Alfred E. Cohn (1879-1957), a young American cardiologist, acquired in London, installed at Mt. Sinai Hospital New York, and used to make these tracings in 1910-1911.
Ref: “Alfred Cohn Dies; Cardiologist, 78,” New York Times (July 23, 1957), p. 25.