The laboratory test, C-Reactive Protein (CRP), has become well established as a marker of inflammation. Recently a high CRP level (indicating an increase in inflammation) was identified as a risk factor for atrial fibrillation. We are conducting this study with patients such as yourself with atrial fibrillation who are planning to undergo cardioversion to determine what sort of relationship exists between CRP levels and atrial fibrillation. We will then look at success rates of converting atrial fibrillation to normal sinus rhythm, compared to patients' CRP levels.