A 26-year-old man with a history of chronic alcohol use is being admitted for inguinal hernia repair:

Negative P waves in lead I, marked right axis deviation, rS pattern in the chest leads, with decreasing voltage from V3 to V6, compatible with dextrocardia with situs inversus. Dextrocardia was confirmed by physical examination and chest X-ray.
For a complete ECG assessment, in patients with dextrocardia the right precordial leads should also be recorded (see ECG 2) 

The right and left arm cables were reversed and the right precordial leads were recorded.  This ECG is normal.