Precordial and posterior chest wall ST-mapping has been utilized in a patient with high anterolateral and true posterior myocardial infarction. In this patient evolution of the anterolateral component of the infarct was accurately delineated by changes in the precordial map which were not detected in the standard precordial leads. The true posterior component of the infarct was clearly diagnosed by detection of pathological Q waves and ST elevations in posterior chest wall maps, whereas right precordial standard leads had shown only suggestive reciprocal changes. The study illustrates the superiority of localized chest wall mapping over conventional 12-lead electrocardiography in detecting transmural infarction in high anterolateral and posterior regions of the left ventricle.