In recent years, radionuclide imaging techniques have gained increasing popularity in clinical practice to evaluate regional myocardial perfusion and viability in patients with acute myocardial infarction who have undergone reperfusion therapy. Myocardial thallium-201 (Tl-201) or technetium-99m methoxyisobutyl isonitrile (Tc-99m Sestamibi) scintigraphy can be used for detecting and localizing areas of necrosis when injected at rest and can be used in conjunction with exercise or pharmacological stress testing for predischarge risk stratification and determining prognosis. In the presence of residual blood flow, uptake of Tl-201 by myocardial cells is not altered unless irreversible membrane injury is present. Postischemic myocardial "stunning" alone does not affect Tl-201 extraction. Tl-201 administered very soon after reperfusion is established may reflect more the hyperemic flow state rather than the degree of myocardial salvage. Initial myocardial uptake of Tc-99m Sestamibi after intravenous injection is also proportional to blood flow. When injected during coronary occlusion, the pattern of uptake of Tc-99m Sestamibi accurately delineates the "area of risk." When injected several hours after coronary reperfusion, the uptake pattern accurately reflects the degree of residual myocardial viability. Serial Tc-99m Sestamibi imaging in patients with myocardial infarction receiving thrombolytic therapy showed that patients with a patent infarct vessel had a significant reduction in defect size compared with prethrombolysis images.