Abstract:Electrocardiogram (ECG) fails to record the dynamic change for short recording time. With wide application of dynamic electrocardiogram, some phenomena are found gradually which were not easily discovered previously. Thus, people pay more attention to these phenomena, including the change of PR interval of I° I atrioventricular block(AVB). It′s a must to give a classification for I° AVB. Here we briefly introduce the classification of I° AVB as well as analyze some examples about it. It′s believed that I° I AVB will be restudied by ECGworkers with the application of dynamic electrocardiogram.