Normal ECG Interpretation

Before you can spot an abnormal ECG, you need to know exactly what normal looks like. Here are the values, shapes, and rhythm that define a normal tracing — and the normal variants that trip people up.

What makes an ECG normal

A normal ECG shows normal sinus rhythm — a P wave before every QRS, upright P waves in lead II, a regular rate of 60–100 bpm, normal intervals, a normal axis, and no abnormal ST-segment or T-wave changes.

Normal values at a glance

Parameter	Normal
Rate	60–100 bpm
Rhythm	Sinus (P before every QRS)
PR interval	0.12–0.20 s
QRS duration	< 0.12 s
QTc	< 0.44 s
Axis	−30° to +90°

Normal wave shapes

• P wave — upright in lead II, smooth and rounded.
• QRS — narrow; a small septal q in lateral leads can be normal.
• ST segment — at baseline (isoelectric).
• T wave — upright in most leads, same direction as the QRS.

Normal variants that look abnormal

• Sinus arrhythmia — rate varies with breathing; normal, especially in the young.
• Benign early repolarization — mild concave ST elevation, often in healthy young adults.
• Isolated voltage criteria — tall QRS without other features may not mean true hypertrophy.
• Septal q waves — small and narrow in lateral leads, not pathologic.

When in doubt, compare with a prior ECG and the clinical picture.

Summary

• Normal = sinus rhythm, 60–100 bpm, normal intervals and axis, no ST-T changes.
• Memorise the normal values so deviations jump out.
• Know the benign variants so you don't over-call abnormality.

Frequently asked questions

What does a normal ECG look like?

Normal sinus rhythm with a P wave before every QRS, a rate of 60–100 bpm, PR 0.12–0.20 s, QRS under 0.12 s, a normal axis, and no abnormal ST-segment or T-wave changes.

What are normal ECG values?

Rate 60–100 bpm, PR 0.12–0.20 s, QRS under 0.12 s, QTc under 0.44 s, and axis between −30° and +90°.

Can a normal ECG have variations?

Yes — sinus arrhythmia, benign early repolarization, small septal q waves, and isolated voltage can all be normal variants.

How do I know if my ECG is normal?

Confirm sinus rhythm, a normal rate, normal intervals and axis, and no ST-T abnormalities; comparison with a prior ECG helps.