Purkinje fibers form the atrioventricular bundle (bundle of His), which is part of the specialized conduction system in the heart. This system generates the stimulus for the heart beat and conducts it to cardiac muscle
Purkinje fibers are modified muscle fibers. They have fewer myofibrils, but a higher content of glycogen. This allows their identification with phosphotungstic acid/hematoxylin (PTAH) stain which reveals cells with fewer myofibrils.
The is at the top of this specimen.
Beneath the endocardium are stained light gray. This lighter staining reflects the lower content of myofibrils in Purkinje cells.
Underneath the Purkinje cells, normal have a darker appearance because of their higher content of myofibrils.