On the advice of William James Mayo, Harrington changed his subspeciality from gastrointestinal and urologic surgery to thoracic and breast surgery. Eventually Harrington developed an international reputation in the diagnosis and treatment of diaphragmatic hernias and mediastinal tumors. He was honored several times by the American Medical Association for work on chronic postpneumonic empyema, and pericardiectomy for chronic constrictive pericarditis. In 1937, Harrington was elected the 20th president of The American Association for Thoracic Surgery and in 1948 he helped found the American Board of Surgery. Harrington came on the staff at Mayo's in 1917 and retired in 1954. He started the department of Thoracic Surgery after a trip to Germany to study thoracotomy methods. He worked with anesthesiologist John Lundy to develop early methods of intubation and anesthesia for open chest cases. Harrington originated the trans-abdominal approach for the repair of hiatal and diaphragmatic hernias. He performed more than 25,000 mastectomies for breast cancer in his long career.
