<prompt> PR interval in ECG denotesIsovolumetric contraction of ventricleInsovolumetric relaxation of heartAtrial contractionNone  <response>: Ans. c Atrial contractionRef: Ganong, 25th edp.525PR intervalFrom the onset of P wave to the beginning of QRS complexDuration - 0.12 to 0.20 secDenotes atrial contraction and Atrioventricular AV conduction time 