EKG Dictionary
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Waves, segments & intervals

RR interval

Also calledR-R interval · RR · cycle length · R-R

Definition

The time between two consecutive R waves (successive QRS complexes), the ventricular cycle length. It is the basis for calculating the ventricular rate: with a regular rhythm at the standard paper speed of 25 mm/s, the heart rate is 300 divided by the number of large squares between consecutive R waves, or 1500 divided by the number of small squares. The RR interval normally varies slightly with breathing (sinus arrhythmia), and irregular RR intervals are one of the defining ECG features of atrial fibrillation.

Sources

  1. Meek S, Morris F. ABC of clinical electrocardiography. Introduction. I: Leads, rate, rhythm, and cardiac axis. BMJ. 2002;324(7334):415-418. doi.org/10.1136/bmj.324.7334.415
  2. Joglar JA, Chung MK, Armbruster AL, et al. 2023 ACC/AHA/ACCP/HRS guideline for the diagnosis and management of atrial fibrillation. Circulation. 2024;149(1):e1-e156. doi.org/10.1161/CIR.0000000000001193

Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.

More in Waves, segments & intervals

Corrected QT (QTc) Delta wave Electrical alternans Epsilon wave Isoelectric line J point J wave (Osborn wave) Low voltage P wave PR interval PR segment Q wave QRS complex QRS duration QRS fragmentation QT interval R wave R wave progression S wave ST segment T wave U wave

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