To identify the presence of viable myocardium in areas of severe systolic dysfunction, we studied 22 patients (age 45 to 78 years) with chronic coronary artery disease and left ventricular dysfunction (mean ejection fraction 29 +/- 9%). All subjects underwent thallium-201 single photon emission computed tomography (SPECT), using the reinjection technique, positron emission tomography (PET) with H2(15)O and 18-fluorodeoxyglucose (FDG) to measure regional blood flow and exogenous glucose uptake, respectively, and nuclear magnetic resonance imaging (MRI). From matched transaxial PET, SPECT and MRI tomograms, a total of 290 left ventricular myocardial regions were analyzed. According to the regional wall thickening, measured from MRI, 3 groups of myocardial regions were identified: akinetic-dyskinetic (n = 60), showing either absence of systolic thickening or systolic thinning; hypokinetic (n = 97), showing an absolute wall thickening less than or equal to 2 mm; normal (n = 133), showing an absolute wall thickening greater than 2 mm. Of the 60 akinetic or dyskinetic regions, 3 were normal by SPECT and 37 corresponded to either a total or partially reversible thallium defect: 34 of these 40 regions also showed presence of FDG uptake by PET. The remaining 20 akinetic or dyskinetic regions showed a thallium defect that remained irreversible after reinjection: in 7 of these 20 regions, however, there was evidence of metabolic activity, as expressed by FDG uptake. Thus, 47 (78%) of the myocardial akinetic or dyskinetic regions showed presence of viable tissue.(ABSTRACT TRUNCATED AT 250 WORDS)