BACKGROUND AND OBJECTIVES: Recently many studies have confirmed positive identification of patients with posterior infarction through ST segment elevation in the electrocardiogram of posterior chest leads V7 through V9. However, the ECG patterns from posterior chest leads in normal adults have not been investigated, so this study was designed to examine such patterns. SUBJECTS AND METHODS: We studied 100 patients with normal conventional 12-lead ECG, normal physical examination and without any history of cardiovascular disease. Leads V7, V8 and V9 were recorded immediately after routine 12-lead ECG at the same horizontal level as that of V6 on the posterior axillary line (lead V7), the posterior scapular line (lead V8), and the left border of the spine (ead V9). RESULTS: The upright P waves in leads V7, V8 and V9 were 99%, 99% and 95% upright, respectively, while the other P waves were isoelectric and none were inverted. The T waves were all upright in leads V7 and V8, while in lead V9, 98% were upright, 2% were isoelectric and none were inverted. None of the subjects had a Q wave duration greater than 0.04 second in any of the 3 leads. At 0.08 second after the J point, only 2 subjects (2%) showed 0.5 to 1.0 mm ST segment elevation, but ST segment elevation was not greater than 1.0 mm in any of the subjects. CONCLUSION: P wave and T wave inversion were absent in all 3 leads. Q wave duration of greater than 0.04 second was also absent in all 3 leads. ST segment elevation was not greater than 1.0 mm in any of the subjects.