- Regular rhythm at a rate of >100 bpm (or age-appropriate rate in children).
- Each QRS complex is preceded by a normal P wave.
- Normal P wave axis: P waves should be upright in leads I and II, inverted in aVR.
- The PR interval remains constant around 120 – 200 ms.
- QRS complexes are < 120 ms wide (unless a co-existent interventricular conduction delay is present).