ECG Interpretation Cheat Sheet

Every number and pattern you need on one page — bookmark or print it for quick reference while you learn to read ECGs.

Grid & calibration

Item	Value
Paper speed	25 mm/s
Small box (width)	0.04 s
Large box (width)	0.20 s
Voltage	10 mm = 1 mV

Rate methods

Method	Formula
300 method (regular)	300 ÷ large boxes between R waves
1500 method	1500 ÷ small boxes between R waves
6-second method (irregular)	QRS in 6 s × 10
Sequence	300, 150, 100, 75, 60, 50

Normal intervals

Interval	Normal
PR	0.12–0.20 s
QRS	< 0.12 s
QTc	< 0.44 s

Rhythm hallmarks

Rhythm	Hallmark
Normal sinus	P before every QRS, 60–100, regular
Atrial fibrillation	Irregularly irregular, no P waves
Atrial flutter	Sawtooth flutter waves
SVT	Narrow, regular, fast (150–250)
VT	Wide, regular, fast
VFib	Chaotic, no organised complexes → defibrillate
Complete heart block	P and QRS dissociated

AV blocks

Block	Hallmark
First-degree	PR > 0.20 s, all conducted
Mobitz I	PR lengthens, then drops a beat
Mobitz II	Constant PR, sudden dropped beat
Third-degree	Complete AV dissociation

STEMI lead groups

Leads	Wall	Artery
II, III, aVF	Inferior	RCA
V1–V2	Septal	LAD
V3–V4	Anterior	LAD
I, aVL, V5–V6	Lateral	Circumflex

See the full method in the ECG interpretation guide.

Frequently asked questions

What should be on an ECG cheat sheet?

The grid/calibration, rate-calculation methods, normal intervals (PR, QRS, QTc), rhythm hallmarks, AV-block patterns, and the STEMI lead groups.

What are the normal ECG values to memorise?

PR 0.12–0.20 s, QRS under 0.12 s, QTc under 0.44 s, and a rate of 60–100 bpm.

Can I print this ECG cheat sheet?

Yes — the page is plain tables designed to print or bookmark for quick reference.