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The current reference standard for differentiating between nonischemic versus ischemic cardiomyopathy (CM) is angiography. The diagnostic accuracy of nuclear stress testing and electron beam tomography (EBT) was evaluated to differentiate between nonischemic and ischemic CM, using coronary angiography as the reference standard.A total of 56 patients who underwent technetium stress testing and coronary angiography for the evaluation of CM were enrolled. Patients then underwent EBT coronary scanning for coronary calcification (CC).Of the 56 patients, 34 (61%) had angiographically significant disease. Using the criteria of ischemia (reversible defect) or infarct (fixed defect) to define a patient with ischemic CM, nuclear stress testing had a sensitivity of 97% (33 of 34 patients) but a specificity of only 18% (4 of 22 patients). Using the criteria of reversible ischemia only, the specificity of nuclear stress testing improved to 50% (P < 0.001); however, the sensitivity decreased to 56%. An EBT score >0 had a sensitivity of 97% (33 of 34 patients) and a specificity of 68% (15 of 22 patients) for defining ischemia. Overall diagnostic accuracy was significantly higher with EBT as compared with nuclear stress testing in this study of patients with reduced ejection fractions (84% vs. 64%; P = 0.009).Given the high sensitivity of nuclear testing and EBT, these tests may prove to be an effective screen before angiography in patients with congestive heart failure of unclear cause.