<P> The Purkinje fibers are further specialized to rapidly conduct impulses (numerous fast voltage - gated sodium channels and mitochondria, fewer myofibrils than the surrounding muscle tissue). Purkinje fibers take up stain differently from the surrounding muscle cells because of relatively fewer myofibrils than other cardiac cells and the presence of glycogen around the nucleus causes Purkinje fibers to appear, on a slide, lighter and larger than their neighbors, arranged along the longitudinal direction (parallel to the cardiac vector). They are often binucleated cells . </P> <P> Heart rate is governed by many influences from the autonomic nervous system . The Purkinje fibers do not have any known role in setting heart rate unless the SA node is compromised . They are influenced by electrical discharge from the sinoatrial node . </P> <P> During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from both the left and right bundle branch to the myocardium of the ventricles . This causes the muscle tissue of the ventricles to contract and generate force to eject blood out of the heart, either to the pulmonary circulation from the right ventricle or to the systemic circulation from the left ventricle . </P> <P> Purkinje fibers also have the ability of firing at a rate of 15 - 40 beats per minute if upstream conduction or pacemaking ability is compromised . In contrast, the SA node in normal state can fire at 60 - 100 beats per minute . In short, they generate action potentials, but at a slower rate than sinoatrial node . This capability is normally suppressed . Thus, they serve as the last resort when other pacemakers fail . When a Purkinje fiber does fire, it is called a premature ventricular contraction or PVC, or in other situations can be a ventricular escape . It plays a vital role in the circulatory system . </P>

The purkinje fibers are responsible for sending the electrical impulse into which area of the heart