This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Gatekeeper of the heart is: 
Select and explain. 
A. SA node, B. AV node, C. Purkinje fibers, D. Bundle of His
B: AV node
Answer: B: AV node 
Explanation: “The AV node is located on the floor of the right atrium. It has an intrinsic firing rate of 40-60 beats per minute. It is known as the gatekeeper of the heart, because it regulates impulses coming from the SA node.”