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If the SA node fails to fire what takes over?
If the SA node fails to fire the atrioventricular node should take over.
What carries electrical impulses across the heart and causes the ventricles contract?
SA node.
The electrical impulse that causes the heart to contract is generated in the right atrium at the?
Sinoatrial, or SA node.
Does the AV node control the heart rate?
Only if the SA Node isn't firing or there is some form of heart block. IIRC, under typical conditions, the SA node fires at 60-70 bpm. If that doesn't happen, or the electrical pathway between the two nodes is broken, the AV node will automatically fire at 50-60 bpm. If that doesn't happen, the ventricles themselves will fire at ~40 bpm. The logic of this system is that each of these nodes will fire on their own, so it is difficult to completely paralyze the heart. At 60 bpm the SA node sends one signal per second, at 50 bpm the AV node waits 1.2 seconds before automatically firing, and at 40 bpm the ventricles wait 1.5 seconds. Because the SA node is fastest, it is usually what paces the rest of the heart. In other words, the AV is a backup pacemaker (among other things).
What is the main pace maker of the heart?
The primary pacemaker of a normal healthy heart is the sinus node (or SA node). It is located in the right atria of the heart.
