Fredrick Arthur Willius (November 24, 1888 – October 19, 1972) was an American research cardiologist and medical historian who was the founding director of the Cardiology section at the Mayo Clinic.

The Willius name (English: /ˈwɪliəs/; German: [ˈvɪlɪʊs]) is a Latinized form of Wille, and the family, which is originally native to Kassel, has borne it since at least the 18th century.

[2][3] Through his father's family, Willius was a third cousin of the scientist Albert Wigand, the general Adolf von Deines, and the physician Georg Ledderhose.

[7] During his third year at the University of Minnesota, he participated in research with James F. Corbett on the causes and pathology of diabetes mellitus, for which he was awarded the Rollin E. Cutts Medal for experimental surgery.

[8] After graduation, Willius entered into a twelve-month internship at the University Hospital, and in 1915, he began his three-year fellowship in surgery at the Mayo Clinic in Rochester, Minnesota.

[11] Plummer and his colleague John M. Blackford had, in 1915, installed at the Mayo Clinic one of the first ECG machines in the country, only five years after Alfred Cohn's successful adoption of the technology at Mount Sinai Hospital in New York City.

Later that year, Blackford left Mayo to help start the Virginia Mason Medical Center in Seattle, Washington, at which point Willius was promoted to head of the lab.

Cardiology was still in its early years as a medical specialty, particularly in the United States, so other doctors throughout the Clinic often asked Willius to consult on their cases involving heart conditions.

[15] Given the youth of cardiology in this nation, much of the early work at the section revolved around creating standards with which to evaluate patients, both in terms of clinical practice, as well as collecting pertinent medical data to advance the field.

While of a similar vein to Willius's first volume, this adopts more holistic approach to the study of history, and focuses on exploring and analyzing the trajectory of the science of medicine as a whole, rather than reproducing verbatim the works of previous scholars.

[7] In 1957, Willius was invited by the Royal College of Surgeons to give a speech on the legacy and contributions of William Harvey to his field of cardiology, and medicine as a whole.

Due to ill health, he was unable to attend the conference, but his speech was delivered in his stead by his friend and colleague Thomas Forrest Cotton.