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Bipolar limb leads (in frontal plane) - I, II, III.

Augmented unipolar limb leads (in frontal plane; require greater amplification) - aVr, aVl, aVf.

Precordial Leads (in horizontal or transverse plane, through AV node; Frank Wilson, Ann Arbor, 1933) - "exploring" electrode on chest -

V1 & V2 overlie RV

V3 & V4 overlie septum

V5 & V6 overlie LV
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