To briefly summarize the components of a normal ECG tracings it consist of waveform components which indicate electrical events during one heart beat. These waveforms are labeled P Q R S T and U.

P wave is the first short upward movement of the ECG tracing. It indicates that the atria are contracting pumping blood into the ventricles.

The QRS complex normally beginning with a downward deflection Q; a larger upwards deflection a peak (R); and then a downwards S wave. The QRS complex represents ventricular depolarization and contraction.

The PR interval indicates the transit time for the electrical signal to travel from the sinus node to the ventricles.

T wave is normally a modest upwards waveform representing ventricular repolarization.