The ECG paper is mostly standardised - Each large square on the paper represents 0.2 seconds - Each small square represents 0.04 seconds - 5 large squares therefore = 1 second - 300 large squares = 1 minute - To calculate heart rate – count large squares within an R-R interval & divide 300 by this number P-waves P-waves represent atrial depolarisation There should be a P-wave preceding each QRS complex QRS complex The QRS-complex represents depolarisation of the ventricles It is seen as 3 closely related waves on the ECG (Q,R & S wave); The first downward deflection is the Q-wave Any upward deflection is an R-wave Downward deflections after an R-wave is called an S-wave It should be between 0.06-0.10 seconds T-wave The T-wave represents ventricular re-polarisation It is seen as a small wave after the QRS complex To Understand More , Check This Photo And Watch This Short Youtube Video :