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
PR interval in ECG denotes ? 
Select and explain. 
A. Isovolumetric contraction of ventricle, B. Insovolumetric relaxation of hea, C. Atrial contraction, D. None
C: Atrial contraction
Answer: C: Atrial contraction 
Explanation: 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.