The diagram indicates purkinje fibres.

The conduction system of the heart is responsible for the synchronised contraction of the atria and ventricles and is comprised of the following main structures:

• Sinoatrial node
• Atrioventricular node
• Atrioventricular bundle of His
• Right and left bundle branches
• Purkinje fibres

The atrioventricular nodes receives signals from the sinoatrial node. The impulses from the atrioventricular node then pass to the Bundle of His and then follow the left and right bundle branches through the interventricular septum and ultimately to the Purkinje fibres which propagate the signal into the ventricles.

Purkinje fibres are located on the inner aspect of the ventricular walls beneath the endocardium in the subendocardium. These fibres have special properties which allow them to conduct action potentials with great efficiency. They are important in ensuring synchronised ventricular contraction. They extend from the interventricular septum, through the papillary muscles and laterally up the walls of the venricles.