the av node and his bundle system were labelled with anti-alpha and anti-beta mab in fetal , newborn , and adult hearts with a double gradient of distribution : spatial ( a higher proportion of alpha-containing fibers in the av node than in the distal portion of the bundle of branches ) and temporal ( a higher proportion of alpha-containing fibers at a given point in fetal development than in the adult heart ) .
C0004247
av node
C0018787
heart