This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Slowest conduction of velocity occurs in \nSelect and explain. \nA. Atrial muscle, B. A. V. node, C. Purkinje fibre, D. Ventricular muscles', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The total delay in the A-V nodal and A-V bundle system is about 0.13 second. This delay, in addition to the initial conduction delay of 0.03 second from the sinus node to the A-V node, makes a total delay of 0.16 second before the excitatory signal finally reaches the contracting muscle of the ventricles.Ref: Guyton and Hall textbook of medical physiology 13th edition. Page:125', 'role': 'assistant'}]