Dr. John Day graduated from medical school at Johns Hopkins University. He did his residency in internal medicine, cardiology, and cardiac electrophysiology fellowship training at Stanford University.

Dr. Day currently serves as head of cardiovascular services for the Mountain Star HCA Healthcare System. He has an extensive clinical practice focusing on atrial fibrillation at St. Mark’s Hospital in Salt Lake City, Utah.

Dr. Day previously served as president of the Heart Rhythm Society and is the immediate past president of the Utah chapter of the American College of Cardiology. He also previously served as the physician leader of Heart Rhythm Services for Intermountain Healthcare. He is recognized as an international thought leader, regularly speaking at medical conferences worldwide on the latest developments in treating atrial fibrillation.

Dr. Day is board certified in cardiology and cardiac electrophysiology. He has published more than 100 manuscripts, abstracts, and book chapters. Dr. Day is the former editor-in-chief of the Journal of Innovations in Cardiac Rhythm Management.

In 2017 Dr. Day published The Longevity Plan: Seven Life-Transforming Lessons from Ancient China, with Harper Collins as publisher. The Longevity Plan was an Amazon number one bestseller and was named a "best book" of 2017 by the Huffington Post and won the Nautilus Book Award Gold Medal for the best book of 2017. Dr. Day’s second book, The Atrial Fibrillation Cure, was also an Amazon bestseller in 2021 and was published by BenBella Books.