This study was performed to determine whether patients with myocardial infarction with apparently reciprocal ST segment depression exhibit abnormal metabolism in zones distant from the primary zone of infarction. Positron emission tomography was performed after the intravenous injection of carbon-11 palmitate in 20 patients with acute myocardial infarction. Infarction was anterior in 7 patients and inferior in 13. Patients with anterior infarction did not show ST segment depression in the inferior leads and all of the patients exhibited normal homogeneous accumulation of palmitate in the inferior and posterior walls. Nine patients with inferior infarction (69%) exhibited ST segment depression (apparently reciprocal or due to anterior wall ischemia) in the anterior precordial leads. Myocardial injury tended to be greater in the primary zone of necrosis among patients with inferior infarction and "reciprocal" ST segment depression compared with those without anterior ST segment depression. This was reflected by the greater total inferior ST segment elevation (0.48 ± 0.35 versus 0.07 ± 0.19 mV [± standard deviation], p < 0.05), peak plasma MB creatine kinase activity (354 ± 134 versus 80 ± 34 IU/liter, p < 0.05) and tomographically estimated infarct size (58 ± 13 versus 33 ± 10 PET-g-eq). Three of the nine patients with inferior infarction and precordial ST depression exhibited anterior tomographic defects underlying the ST segment depression. Thus, although most of the patients with inferior infarction and precordial lead ST segment depression had no anterior wall metabolic compromise (67%) indicating that the anterior ST segment changes were truly reciprocal phenomena, in some the precordial electrocardiographic abnormalities reflected impaired metabolism in the anterior wall indicative of ischemia.