Second-degree AV block is a heart condition in which the electrical activity of the heart is abnormally high, with partial interruption of conduction from the atria to the ventricles and delayed atrioventricular conduction. There are two types of AV block: second degree type I AV block and second degree type II AV block, which have different causes. When the symptoms of AV block are mild, there is no typical clinical manifestation, and occasionally you may feel panic and shortness of breath. The diagnosis of second degree AV block can be made based on the patient’s age, medical history, symptoms, signs and ECG.