Cardiac muscle control
The process starts in the SAN which is in the wall of the right atrium. The SAN is like a pacemaker, it sends regular waves of electrical activity to the atrial walls.
This causes both ventricles to contract at the same time!
The non-conducting collagen tissue prevents waves being passed directly from the atria to the ventricles.
The waves are transfered from the SAN to the AV node.
The AV node is responsible for passing the waves onto the bundle of His. But before this happens there is a slight delay to make sure the ventricle contracts after the atria have emptied.
The bundle of His is a group pf muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right & left ventricle walls called the Purkyne fibres.
The Purkyne fibres carry the waves into the muscular walls of both ventricles causing them to contract simultaneously, from the bottom up.