The QRS complex is the most prominent element of the electrocardiogram: it reflects depolarization (electrical excitation) of both ventricles of the heart and coincides with their contraction. It consists of the Q, R and S waves.
The width of the QRS shows how quickly the impulse travels through the ventricular conduction system, and it is assessed together with the QT interval and other ECG parameters.
Reference ranges
The duration (width) of the QRS is measured in milliseconds from the start of the Q wave to the end of the S wave:
| Normal | 80 – 100 ms |
| Narrow (supraventricular) complex | < 120 ms |
| Wide complex | ≥ 120 ms (0.12 s) |
What an elevated level means
A wide QRS (≥120 ms) means the impulse travels through the ventricles more slowly than usual. Causes include bundle branch blocks, ventricular rhythms and extrasystoles, WPW syndrome, hyperkalemia, and the effect of certain drugs. A high QRS amplitude (voltage) is a sign of left ventricular hypertrophy.
What a low level means
A narrow QRS (<120 ms) is normal: ventricular excitation travels along the usual fast pathways, and the rhythm is supraventricular. Low voltage of all complexes occurs with obesity, pericardial effusion, and hypothyroidism.
How the test is done
The width is measured on a 12-lead ECG, choosing the lead with the widest complex. The assessment is always compared with the QRS shape across different leads.
What affects the value
- Incorrect recording speed or calibration of the strip.
- Artifacts from movement, tremor, or poor electrode contact.
- Tachycardia can mask the true width of the complex.
Calculate using this marker
Calculators where QRS complex is used directly:
Frequently asked questions
What does a wide QRS complex mean?
A QRS wider than 120 ms indicates slowed conduction through the ventricles — most often a bundle branch block, a ventricular rhythm or electrolyte disturbances. A cardiologist's assessment is needed.
Is a QRS of 110 ms normal?
Yes, it is within the normal range (normal is 80–100 ms, up to 120 ms is a borderline zone). An isolated value with no other changes is usually not dangerous.