The electrocardiograms of patients with emphysema may suggest associated old anterior myocardial infarction. Sixteen patients with the physiological characteristics of emphysema were studied, who also showed poor R wave progression in the anterior chest leads, so that RV3 was less than or equal to 4 mm. A thallium-201 cardiac scan consistent with previous anterior (septal) myocardial infarction was present in seven patients. In these patients there was no significant increase in RV3 amplitude when recorded one interspace below the conventional site. In the nine patients with a thallium-201 cardiac scan negative for old anterior myocardial infarction, RV3 amplitude increased from 2.2 +/- 0.4 mm to 6.4 +/- 1.2 mm. Patients with or without associated old anterior myocardial infarction could be better diagnosed by consideration of RV3 amplitude as recorded from one interspace lower, as compared with conventional electrode placement. All five patients with RV3 (lower interspace) less than 2 mm had associated anterior infarction, and all seven patients with RV3 (lower interspace) greater than 3 mm did not. This simple manoeuvre is recommended in patients with emphysema and an electrocardiogram suggestive of old anterior myocardial infarction.