The accuracy of stress single photon emission computed tomography (SPECT) is limited by imaging artifacts, many of which are caused by soft tissue attenuation. A recent multicenter study performed by our laboratory comparing 7 commercially available attenuation correction (AC) camera systems in a cardiac phantom showed the best performance with the GE Hawkeye (a hybrid gamma camera-CT scanner) and the University of Michigan M-step (unique feature a camera orbit of 360˚ versus the usual 180˚) systems. In this study we will combine the strengths of these two systems (GE Hawkeye AC system and 360˚ camera orbit) to test the accuracy of this imaging system in a population of 400 consecutive patients undergoing clinically indicated stress SPECT. These patients will undergo SPECT imaging both with conventional methodology and the GE Hawkeye system. The conventional study will be interpreted and reported in the usual clinical fashion. The GE Hawkeye images will be interpreted independently by 2 observers blinded to the results of conventional imaging and will not be reported clinically. The primary study hypothesis is that AC will substantially reduce attenuation artifacts (mild fixed defects) without reducing the accuracy of either normal studies or myocardial infarction (MI). Clinical data and noninvasive test results (history of MI, electrocardiogram, and gated wall motion) will be used to distinguish defects which represent attenuation (false-positive) versus those due to MI (true-positive).