Atrial fibrillation (AF) is growing into an epidemic affecting 1 in 4 adults. There is a need for research to elucidate the prevalence of ischemic cardiomyopathy in patients diagnosed with AF. The objective of this study is to demonstrate the utility of MRI in assessment of coronary artery disease. The specific objective is to demonstrate sensitivity/specificity comparable to that reported in meta-analyses of non-AF patients and adenosine (90% /80%) in an AF population using the time-efficient vasodilator regadenoson that requires only a single intravenous (IV).