The manifestations of second-degree AV block in babies mainly include dizziness, fatigue, shortness of breath and palpitations (rapid heartbeat, often accompanied by panic). Babies with second-degree AV block are categorized into type I and type II. Both type I and type II second-degree AV block may have no conscious symptoms, and there may be dizziness, chest tightness, fatigue, palpitations when the heart rate is slow, shortness of breath when the activity is strenuous, and there may also be a sudden appearance of cyanosis or pallor of the skin. Type II second-degree AV block may present with syncope, angina pectoris, and heart failure in severe cases. Type I is more common than Type II, but the prognosis for Type II is more serious, and it is likely to progress to complete AV block, resulting in A.S. syndrome. Babies with signs of second-degree AV block should go to the hospital in time and be treated under the guidance of a doctor.