If the SA node does not function properly and is unable to control
the heart rate, a group of cells further down the heart will become the ectopic pacemaker of the heart. These cells form the atrioventricular node (or AV node),
which is an area between the left atrium and the right ventricle within
the atrial septum, will take over the pacemaker responsibility.
The cells of the AV node normally discharge at about 40-60 beats per minute, and are called the secondary pacemaker.