How to read a normal ECG (rate, rhythm, intervals)
Other platforms explain it with text and video. In VMS you practice it on the patient.
A fixed routine lets you read any ECG quickly and miss nothing. Knowing normal values first makes every abnormal pattern easier to see.
Step by step
Check the basics
Confirm patient name, date and time. Check the standard settings: paper speed 25 mm/s and 10 mm per mV. [1]
Find the rate
For a regular rhythm, divide 300 by the number of large boxes between two R waves. For an irregular rhythm, count QRS complexes in 6 seconds and multiply by 10. [2]
Confirm the rhythm
Sinus rhythm has a P wave before every QRS, a QRS after every P wave and upright P waves in lead II. [2]
Measure the intervals
Measure the PR interval, QRS width and QT interval in small boxes. Each small box is 0.04 seconds. [2]
Check the axis
If the QRS is mainly upright in leads I and aVF, the axis is normal. [2]
Look at ST and T waves
Scan every lead for ST elevation or depression and for T waves that are inverted or very tall. [2]
Compare and report
Compare with an old ECG and state rate, rhythm, intervals, axis and any changes in one clear summary. [1]
Common errors
- Using the 300 rule on an irregular rhythm.
- Accepting the machine reading without checking it.
- Not comparing with a previous ECG.
Typical adult values [2]
| Measure | Normal | In small boxes |
|---|---|---|
| Heart rate | 60 to 100 per minute | 3 to 5 large boxes between R waves |
| PR interval | 0.12 to 0.20 seconds | 3 to 5 small boxes |
| QRS width | Under 0.12 seconds | Under 3 small boxes |
| QTc | Under about 450 ms (men) or 460 ms (women) | QT usually less than half the R to R distance |
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. VMS is not affiliated with these organizations. Updated: 2026-10-11.