The Normal ECG: Waves, Intervals and Normal Values

By the DecodeMed TeamOctober 19, 20267 min read

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A normal adult ECG shows sinus rhythm at 60–100 bpm, a PR interval of 120–200 ms, a QRS under 120 ms, a QTc under about 450 ms in men and 460 ms in women, an axis between −30° and +90°, an isoelectric ST segment and upright T waves in I, II and V3–V6. Values vary slightly between references.

Normal 12-lead ECG in the DecodeMed ECG atlas, with the P waves, QRS complexes, ST segments and T waves coloured in every lead and a lead II rhythm strip — A real normal 12-lead ECG in the ECG atlas: each wave is coloured where cardiologists marked it. Tracing: LUDB, PhysioNet (ODC-BY 1.0). Image sources and licences.

Normal values at a glance

Measure	Typical normal value (adult)	Where to look
Heart rate	60–100 bpm	Rhythm strip
P wave	Under 120 ms and under 2.5 mm tall	Lead II, V1
PR interval	120–200 ms	Lead II
QRS duration	Under 120 ms (usually 80–110)	Widest lead
QTc	Under about 450 ms (men), 460 ms (women)	Lead II or V5
Axis	−30° to +90°	Limb leads
R-wave transition	V3–V4	Chest leads

P wave and PR interval

Sinus P waves are upright in I, II and aVF and inverted in aVR. In V1 the P wave is often biphasic.
A wide or notched P suggests left atrial enlargement; a tall P in II suggests right atrial enlargement.
PR over 200 ms is first-degree AV block; under 120 ms raises pre-excitation or a low atrial rhythm.

QRS complex

Width: 120 ms or more is a bundle branch block, ventricular rhythm or pacing until proven otherwise.
Small septal q waves are normal in I, aVL, V5 and V6. A Q wave of 40 ms or more, or deeper than a quarter of the R wave, is pathological.
R-wave progression: the R wave grows from V1 to V6 and equals the S wave around V3–V4.

ST segment, T wave and QT

ST segment: at the baseline, measured at the J point. A small ST elevation in V2–V3 can be normal, especially in young men.
T waves: upright in I, II and V3–V6, inverted in aVR; they can be inverted in III, aVL, aVF and V1 in healthy people.
QT: varies with rate, so correct it (QTc). A QTc over 500 ms carries a high risk of arrhythmia.
U wave: a small wave after the T, best seen in V2–V3, can be normal.

A 12-lead ECG being drawn in real time at 25 mm/s in the DecodeMed ECG atlas, with the sweep line halfway across the paper — Play mode in the ECG atlas draws the real tracing at 25 mm/s, as on a monitor. Tracing: LUDB, PhysioNet (ODC-BY 1.0). Image sources and licences.

Normal variants that are not disease

Sinus bradycardia in athletes and during sleep.
Sinus arrhythmia: the rate rises with inspiration and falls with expiration.
Early repolarisation: J-point elevation with a notch or slur, common in young people.
A right axis in children and some slim young adults.

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See it on a real tracing

Every value above appears on real tracings in the ECG atlas, with each wave coloured where cardiologists marked it and the intervals measured. To read in order, follow how to learn ECG from scratch; for rate and axis, see heart rate and axis.

Frequently asked questions

What is the normal PR interval?

120 to 200 ms (3 to 5 small squares at 25 mm/s).

What is a normal QRS duration?

Under 120 ms, usually 80 to 110 ms. 120 ms or more is a wide QRS.

What is a normal QTc?

Under about 450 ms in men and 460 ms in women; over 500 ms is high risk. Cut-offs vary slightly between guidelines.

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