S1, caused by the atrioventricular valves closing, at the beginning of systole, and S2, caused by the aortic and pulmonary valves closing, at the beginning of diastole.
In this form, the great arteries still connect to the wrong ventricle, but it's just that the ventricles are the one's that switch places along with their atrioventricular valves.
This so-called " group beating" can be differentiated from a type 1 second-degree atrioventricular heart block by identifying the abnormally shaped p-waves that are characteristic of an atrial ectopic focus.
The impulses leap across synapse-like connections between the cells called gap junctions, and continue down the conduction system until they reach the atrioventricular node, or AV node, located just above the tricuspid valve.
The path the electrical impulse takes to the bottom of the heart is called the atrioventricular bundle, also known by the more rad name, the bundle of His, where it branches out to the left and right ventricles.
It's then delayed just slightly as it goes through the atrioventricular or AV node, before it passes through the Bundle of His and to the Purkinje fibers of the left and right ventricles, causing them to contract as well.