ECG rhythms Sinus rhythms
Normal sinus rhythm ECG
Normal sinus rhythm. Regular rhythm at 60–100/min, an upright P wave before every narrow QRS, and a constant normal PR.
A 30-second recording of the heart model, played in real time. Run live starts the engine itself with this rhythm.
Computed by the TracingsMD heart model (Junkers engine): simulated for education, not a patient recording and not for diagnosis.
Measured on this recording
| Ventricular rate | 72/min |
|---|---|
| PR | 158 ms |
| QRS | 84 ms |
| QT | 355 ms |
| QTc (Bazett) | 390 ms |
| QTc (Fridericia) | 378 ms |
What it is
The normal heart rhythm. Each beat starts in the sinus node, spreads through the atria (P wave), is delayed briefly in the AV node (PR interval) and activates both ventricles quickly through the His–Purkinje system (narrow QRS), at 60–100/min, with a PR of 120–200 ms and a QRS under 120 ms. Most texts use 60–100/min; the 2018 ACC/AHA/HRS guideline also counts 50–59/min as normal.
How to read this strip
| Rate | 60–100/min. |
|---|---|
| Rhythm | Regular. |
| P waves | Upright in II, one before every QRS. |
| PR | Normal and constant. |
| QRS | Narrow (under 120 ms). |
| QT | Normal for the rate. |
Normal variation
- The rate rises with exercise and emotion, and falls with rest, sleep and physical fitness; fever and pain also raise it.
- Small breath-to-breath RR changes (respiratory sinus arrhythmia) are normal, especially in young people.
What to consider
- A normal rhythm does not exclude heart disease: still read the axis, ST segments, T waves and QT on a 12-lead ECG.
- Compare with earlier ECGs: a new change in an otherwise normal tracing can matter.
- Match the monitor to the patient: an organized rhythm without a pulse is pulseless electrical activity (PEA).
Key point
Read every strip in the same order: rate, rhythm, P waves, PR, QRS, QT. A normal strip read this way builds the reference for every abnormal one.
Not to be confused with
- Sinus bradycardia — The rate is not below 60/min.
- Sinus tachycardia — The rate is not above 100/min.
- First-degree AV block — The PR interval is normal, not longer than 200 ms.