Atrial fibrillation is common, affecting 2.2 million Americans and is likely to increase with the aging of the US population. The most devastating sequelae of atrial fibrillation is stroke. National guidelines recommend warfarin, an oral anticoagulant for patients with atrial fibrillation and multiple risk factors (e.g., hypertension, diabetes, older age, stroke or TIA, heart failure) to reduce the stroke risk. Veterans prescribed warfarin are usually managed closely in anti-coagulation clinics. Pharmacists staff these clinics, coordinating blood draws, titrating warfarin dose to maintain therapeutic INR levels, and re-enforcing adherence to therapy. Prior meta-analysis suggests that patients on warfarin managed in these clinics have better anticoagulation control compared to patients followed in non-specialized clinics.