In general, the DefensePlanning Guidance tells the Army what missions and scenarios to or-ganize and train for. Internal Army processes lead to decisions aboutspecific types of units to create, whether those units should be re-serve or active, and whether those units should be resourced fully orat some lower level.
There are actually two pacemakers. The SA node is the primary; the atrioventricular node (AV node), located in a bundle of tissues on the border between the right atrium and the right ventricle, is the secondary. When the SA node sends out an electrical impulse, the first place it goes is to the AV node. While the SA node sets the rhythm of your pulse, the AV node sets the rhythm of your heart contractions. It delays the signal on its way to the ventricle, giving the atrium time to contract first.
The atrioventricular valves are two of the four valves within the heart, the other two valves being the semilunar valves. The atrioventricular valves are located between the the atria and the ventricles of the heart. The atrioventricular valve between the left atrium and the left ventricle is called the bicuspid valve (also known as the mitral valve), and the atrioventricular valve between the right atrium and the right ventricle is called the tricuspid valve.