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 the physician executive of cardiovascular services for the Mountain Star HCA Healthcare System. He has a large clinical practice focusing on atrial fibrillation at St. Mark's Hospital in Salt Lake City, Utah. Dr. Day warmly welcomes new atrial fibrillation patients into his practice.

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 atrial fibrillation medical conferences around the world, on the latest developments in the treatment of 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 best seller and was named best books 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, will be published on February 16, 2021 by BenBella Books.

Dr. Day is married and has four children ages four to 18. He and his family loves to snow ski and go to Lake Powell every chance they can. He also loves mountain biking, trail running, and backcountry skiing.