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
[{'content': 'Gatekeeper of the heart is: \nSelect and explain. \nA. SA node, B. AV node, C. Purkinje fibers, D. Bundle of His', 'role': 'user'}, {'content': 'Answer: B \nExplanation: “The AV node is located on the floor of the right atrium. It has an intrinsic firing rate of\xa040-60 beats per minute. It is known as the gatekeeper of the heart, because it regulates\xa0impulses coming from the SA node.”', 'role': 'assistant'}]