The purpose of the research is to compare two strategies for treating atrial fibrillation or atrial flutter, both of which are referred to as AF, after cardiac surgery. AF is the most common complication after cardiac surgery. AF is when the upper chambers of the heart (atria) experience disorganized electrical activity which causes the heart beat to be irregular. The two treatment strategies to be used in this study are called rhythm control and rate control. The rhythm control strategy will attempt to bring the heart beat back to a regular rhythm using treatments known and approved to control heart rhythm. The rate control strategy will attempt to bring the heart rate to less than 100 beats per minute at rest using medications known and recommended to control heart rate. Both strategies are commonly used to treat AF. All of the medications that will be used in this study are the standard of care for use in patients experiencing AF. This research seeks to determine whether rhythm control is better than rate control in patients with AF after cardiac surgery.