 Absolute myocardial blood flow MBF and myocardial flow reserve MFR are calculated measurements that are obtained using positron emission tomography PET nuclear imaging, from a myocardial perfusion imaging MPI stress test, due to the advanced capabilities of the PET camera technology. These calculations provide more diagnostic and prognostic information for patients. Single photon emission computed tomography SPECT nuclear imaging is more widely done due to the availability and lower costs, but in the past has not been able to provide the additional information needed to perform the MBF and MFR calculations. SPECT cameras have now been developed and are in use, as well as software for the cameras that have shown that these measurements can be obtained from SPECT. The goal of this study is to compare SPECT and PET measurement of MBF and MFR and determine the reproducibility of SPECT MFR measurements. 