Patient-specific variables that influence the response to beta-blockers include comorbid conditions, weight, age, and level of physical activity. Ethnic differences in the response to beta-blockers for the treatment of HTN and HF are well-described. However, the contribution of genetic variants to beta-blocker efficacy in AF is unknown. We propose to study, using a candidate gene approach, the effect of genetic variants on heart rate response to beta-blockade in patients with AF.