Atrial fibrillation is the most common arrhythmia and carries a substantial risk for embolic stroke which can be significantly mitigated by anticoagulant therapy. In this chapter, we review the epidemiology of atrial fibrillation and the biologic antecedents leading to atrial fibrillation. We then comment on the interaction between atrial fibrillation and atrial cardiopathy. We will explore the question of whether atrial cardiopathy alone can produce embolic stroke. We hope the reader will then focus on the expanding surge of atrial fibrillation closely aligned with the increasing burden of embolic stroke. There are additional cardioembolic strokes that appear to occur in the presence of atrial cardiopathy without the onset of atrial fibrillation. Promising new markers are available for predicting atrial cardiopathy and hence guiding treatment for initiation of DOACs. This has the potential to prevent many embolic strokes before they occur. Another missed clinical opportunity is aggressively targeting diastolic dysfunction with ACE-I, AT2 blockers, and MRAs to prevent the development of advanced atrial cardiopathy and subsequent embolic stroke and atrial fibrillation.