What a normal 12-lead looks like and what to expect in every lead. Every abnormal ECG in this guide is shown next to this one.

Ilateral

P up, QRS up, T up. With aVF it gives the axis.

aVRright / “nobody’s lead”

Everything negative — P, QRS, T. Upright aVR = suspect lead reversal.

V1septal

Small r, deep S. P can be +/−. T can be flat/inverted — still normal.

V4anterior

R now bigger than S.

IIinferior

Best lead for P waves and rhythm — P clearly upright.

aVLhigh lateral

Smaller QRS, can be +/−. Small q is fine.

V2septal

rS, r a bit taller than V1. T upright.

V5lateral

Tallest R, tiny septal q, upright T.

IIIinferior

Most variable — small, biphasic QRS, small q or flat/inverted T can be normal.

aVFinferior

P, QRS, T upright (thumb up for axis).

V3anterior

Transition: R ≈ S (V3–V4).

V6lateral

Tall R (a bit less than V5), small q, T up.