In this quick easy-to-understand lesson, we learn about atrial fibrillation, causes, symptoms, diagnoses, and treatments for USMLE medicine. Atrial fibrillation is the most common type of cardiac arrhythmia. This means the heart beat has an irregularly irregular rhythm. Symptoms can include fatigue, dyspnea (difficulty breathing), and heart palpitations in the chest. You diagnose atrial fibrillation via EKG. It can be treated with medications or surgically.