Atrial fibrillation is a common heart rhythm disorder that increases the risk of stroke. In patients with atrial fibrillation, blood clots most often form in a small structure of the heart called the left atrial appendage. If a blood clot travels from the heart to the brain, it can cause a stroke. Blood-thinning medications are commonly prescribed to reduce the risk of stroke in patients with atrial fibrillation. However, some patients cannot take these medications long-term because of bleeding risk, side effects, or other medical reasons. Closing the left atrial appendage is an alternative approach to reduce the risk of stroke by preventing blood from collecting in this area. When patients undergo cardiac surgery for another indication, closure of the left atrial appendage can be performed during the same operation. This study is designed to evaluate the safety and effectiveness of surgical closure of the left atrial appendage using a device called AtriLASH during cardiac surgery. AtriLASH is a surgical suture-based device intended to close the left atrial appendage. The study will assess whether the left atrial appendage can be safely and effectively closed using this method in patients with atrial fibrillation undergoing cardiac surgery. The information obtained from this study may help determine whether this approach can reduce the risk of stroke and potentially decrease the need for long-term use of blood-thinning medications in selected patients.