Normal EKG tracings consist of waveform components that indicate electrical events during one heart beat. These waveforms are labeled P, Q, R, S, T and U. The following descriptions are with respect to Lead II.
P wave is the first deflection and is normally a positive (upward) waveform. It indicates atrial depolarization.
QRS complex follows the P wave. It normally begins with a downward deflection, Q; a larger upward deflection, R; and then a downward S wave. The QRS complex represents ventricular depolarization and contraction.
T wave is normally a modest upward waveform, representing ventricular repolarization.
U wave indicates the recovery of the Purkinje conduction fibers. This wave component may not be observable.