Abstract: The fibrous tissue and fatty tissue in the cardiac conduction system of 230 Chinese of Han Nationality were measured semiquantitatively. The tissue sections were stained by H&E stain and partly by Masson trichrome method. The cases were divided into 8 age groups. According. to the amount of the mesenchymal tissues, they were classified into Grade I(<25%), Grade Ⅱ (26%-50%) and Grade Ⅲ(>50%). The results were analyzed statistically which showed that in sino-atrial node (SAN ) and His nbundle (HB), the appearance of fibrous and fatty tissue began from 40 years of gee; in atrioventricular node (AVN), fat appeared from 30 years of age while fibrous tissue began from 60. All of these increased with further increase of age. The delineation of natural change and pathological changes were discussed'

Key words: cardiac conduction system, age related changes, mesenchymal tissue