If electricity flows toward the positive electrode, the patterns produced on the graph paper or oscilloscope are upright, if the electricity flows toward the negative electrode, the patterns produced on the graph paper or oscilloscope are inverted. The graph paper is standardized to allow for comparative analysis of EKGs.

A cardiac cycle includes everything from depolarization of the atria through repolarization of the ventricles. A single cardiac cycle should produce a coordinated cardiac contraction and generate a pulse.

The P wave is the typically the first wave present before a QRS complex and represents atrial depolarization. In Lead II they should be upright, uniform, round, and have a one-to-one relationship with the QRS complex. The next area is the PR segment or PR interval; this is measured from the beginning of the P wave to the beginning of the QRS. The normal value for a PRI is 0.12 - 0.20 seconds. The PR segment represents the delay in the conduction at the AV node. The QRS complex represents the depolarization of the ventricles. It is comprised of the Q wave, the R wave, and the S wave. The Q wave is the first negative deflection following the P wave. Not all EKGs will have a Q wave. The R wave is the first positive deflection following the P wave. The S wave is the first negative deflection after the R wave. The QRS is measured from the beginning of the Q wave to the end of the S wave. A normal QRS complex is <0.12 seconds. The T wave is the next deflection (positive or negative) following the QRS. The segment between the S wave and the T wave is called the ST segment.