Myocardial perfusion imaging provides important prognostic information in patients with known or suspected coronary artery disease (CAD) and sustained myocardial infarction. The combination of several scintigraphic variables allows separation of patients at low and high risk for future events. In patients with known or suspected CAD, myocardial perfusion imaging has been demonstrated to provide incremental information over clinical, exercise ECG and angiographic data. Also, an increase in referral-rate for cardiac catheterization and revascularization, paralleling the increase in severity of abnormalities on myocardial perfusion imaging, was observed. Perfusion imaging results appear to be interpreted and implemented appropriately in the diagnostic work-up and subsequent treatment of patients with known or suspected CAD. Therefore, myocardial perfusion imaging may serve as a gatekeeper for more costly and invasive procedures. With the introduction of gated SPECT imaging, it is now possible to assess both perfusion and left ventricular function simultaneously. It is anticipated that gated SPECT imaging will provide very strong prognostic data.