 Atrial fibrillation AF is the most preventable cause of stroke. CHADS and CHA2DS2VASc scores predict the likelihood of stroke in patients with nonvalvular AF. Atrial flutter confers a similar risk of stroke as atrial fibrillation. Anticoagulant therapy with warfarin, dabigatran, rivaroxaban, apixaban, and edoxaban is effective for prevention of thromboembolic stroke in most patients with AF. However, despite widely available risk stratification tools, five options for anticoagulation, and evidence-based practice guidelines, thromboprophylaxis for stroke prevention in AF is under-prescribed in the U.S., Europe, and worldwide. The investigators have previously demonstrated the efficacy of an alert-based computerized decision support CDS strategy for prevention of symptomatic venous thromboembolism VTE in at-risk hospitalized patients not receiving any thromboprophylaxis. The investigators goal is to create and evaluate an alert-based CDS strategy for stroke prevention in patients with nonvalvular AF or atrial flutter in a randomized controlled trial. The investigators have the following specific aims: 