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': 'PR interval in ECG denotes ? \nSelect and explain. \nA. Isovolumetric contraction of ventricle, B. Insovolumetric relaxation of hea, C. Atrial contraction, D. None', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Atrial contractionPR interval represents atrial depolarization (atrial contraction) and condution throught AV nudeElectrocardiogram Normal ECG in a bipolar limb leads typically shows five waves named P, Q, R, S and T. Q, R and S waves are collectively called QRS complex.", 'role': 'assistant'}]