PR interval

In electrocardiography, the PR interval is the period, measured in milliseconds, that extends from the beginning of the P wave (the onset of atrial depolarization) until the beginning of the QRS complex (the onset of ventricular depolarization); it is normally between 120 and 200 ms in duration.

The PR interval is sometimes termed the PQ interval.

Variations in the PQ interval can be associated with certain medical conditions:

Schematic representation of a normal sinus rhythm EKG wave
PQ segment divided into parts corresponding to the location in heart's electrical conduction system