This 61-year-old man is admitted to the cardiac ward with angina:

• Sinus rhythm
• Chest lead misplacement (V1-V3 lead reversal)
• ST elevation in V1-V4 – Consider early repolarization or injury (clinical assessment is indicated)

The finding of a diphasic (plus-minus) P wave in V3 and positive P in V1 strengthens the suspicion that V1 and V3 have been reversed. Misplacement and/or reversal of chest leads is common, particularly in hospital areas where a large number of ECGs are recorded. The digitized computer system misdiagnosed this tracing as “septal infarction” because of the decrease of the R wave voltage from V1 to V3.