Atrial fibrillation is also called atrial fibrillation, while third-degree atrioventricular block causes a heart rate of less than 55 beats per minute. Once atrial fibrillation with third-degree is present, the diagnosis is mainly made by the electrocardiogram, which shows the absence of P waves in each lead and the absence of a rhythm in the heart rate. In addition, a slow heart rate, usually below 55 beats per minute, can be diagnosed as atrial fibrillation combined with third degree AV block, as well as coronary artery lumen narrowing due to atherosclerotic heart disease, so all diagnoses are also clarified by cardiac ultrasound and coronary CTA, and then active treatment is given.