The use of electrocardiograms in the study of heart conditions began at Mayo by Dr. John Blackford under Dr. Henry Plummer's supervision. After inaugurating the service, Dr. Blackford trained Dr. Fredrick Willius, a new clinic fellow, to assist him in 1915. Dr. Willius took over the laboratory in 1917.

In 1922, Dr. Willius established a section on medicine with a special interest in cardiology. Mayo's first electrocardiograph unit was ordered from England in 1912. The Cambridge device did not arrive until 1914 because it was custom-made and required considerable assembly time. Early users of the instrument remembered that it was large, slow to use, and had a complicated optical assembly that was subject to alignment problems.

The Cambridge electrocardiograph was the fundamental equipment in the new laboratory, located on the third floor of the 1914 Building. It was installed in a dark room. Electrodes were attached to the patient's limbs, which rested in shallow metal pans containing a concentrated saline solution. After the reading was taken, the glass photographic plate on which it had been recorded went to the Section on Photography for processing and then returned to the Electrocardiographic Laboratory for interpretation.

The is part of a rich history in cardiovascular care at Mayo Clinic.