This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Conducting System of Hea, Subject name: Physiology
[{'content': 'If the Purkinje fibers, situated distal to the A-V junction, become the pacemaker of the hea, what is the expected hea rate? \nSelect and explain. \nA. 30/min, B. 50/min, C. 60/min, D. 70/min', 'role': 'user'}, {'content': 'Answer: A \nExplanation: If the Purkinje fibers are the pacemaker of the hea, the hea rate ranges between 15 and 40 beats/ min. In contrast, the rate of firing of the A-V nodal fibers are 40 to 60 times a minute, and the sinus node fires at 70 to 80 times per minute. If the sinus node is blocked for some reason, the A-V node will take over as the pacemaker, and if the A-V node is blocked, the Purkinje fibers will take over as the pacemaker of the hea.', 'role': 'assistant'}]