<prompt> A-H interval on ECG is for conduction -Through His-Purkinje systemFrom AV node to bundle of HisFrom Purkinje system to ventricular fibresThrough ventricular fibers  <response>: Ans. is b i.e., From AV node to bundle of Hiso Certain intervals are measured to provide information regarding AV block.PA interval: It is time taken from onset of P-wave to onset of deflection in atrial catheter. It is an index of intra-atrial conduction. Normal vlaue is less than 55 mS.AH interval : it represents conduction through AV node, i.e., conduction from AV node to bundle of His. Normal vlaue is less than 130 mS.HV interval : It represents conduction through His-Purkinje system, i.e., conduction from His-Purkinje system to ventricular muscle fibers. Normal value is less than 50 mS. 