Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Purkinje fibers (or Purkyne tissue) are located in the inner ventricular walls of the heart, just beneath the endocardium. These fibers are specialized myocardial fibers that conduct an electrical stimulus or impulse that enables the heart to contract in a coordinated fashion.
Because of their specializations to rapidly conduct impulses (numerous sodium ion channels and mitochondria, fewer myofibrils than the surrounding muscle tissue), Purkinje fibers take up stain differently than the surrounding muscles cells, and on a slide, they often appear lighter and larger than their neighbors.
Purkinje fibers work with the sinoatrial node (SA node) and the atrioventricular node (AV node) to control the heart rate.
During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from the left and right bundle branches to the myocardium of the ventricles. This causes the muscle tissue of the ventricles to contract and force blood out of the heart — either to the pulmonary circulation (from the right ventricle) or to the systemic circulation (from the left ventricle).
The impulse through the Purkinje fibers is associated with the QRS complex.
Purkinje fibers also have the ability of automaticity - they generate action potentials, but at a slower rate than sinoatrial node and other atrial ectopic pacemakers. Thus they serve as the last resort when other pacemakers fail.
They were discovered in 1839 by Jan Evangelista Purkinje, who gave them his name.