In this Cardiovascular Grand Rounds presentation, Peter A. Noseworthy, M.D., a cardiac electrophysiologist at Mayo Clinic's campus in Rochester, Minnesota, discusses the use of observational data to close the gap between clinical trials and clinical practice, specifically related to the use of nonvitamin K oral anticoagulants (NOACs) for the prevention of cardioembolic stroke in patients with atrial fibrillation.