His book titled Clinical Cardiac Electrophysiology: Techniques and Interpretations is widely acknowledged as the definitive treatment of the discipline.

He served as Herman Dana Professor of Medicine at Harvard Medical School, director of the Harvard-Thorndike Electrophysiology Institute and Arrhythmia Service[1] and the chief of cardiology at Harvard University's Beth Israel Deaconess Medical Center in Boston.

[4] After spending two years as a research associate with Anthony Damato at the Staten Island Public Health Service Hospital, he published articles on the electrophysiologic basis and anatomic location of AV nodal reentry and map-guided subendocardial resection to cure ventricular tachycardia, a procedure Time dubbed "the Pennsylvania Peel" in honor of the Penn cardiology department's surgical innovation.

[4] Josephson's work helped to transform electrophysiology from a research field to a powerful clinical discipline for treating patients.

[5] Josephson worked closely over the years with European cardiac electrophysiology pioneer Hein Wellens, chief of cardiology emeritus at the University of Limburg in Maastricht, Netherlands.