A SPECT rest image will be obtained using a technetium based isotope. On a separate day, a Rubidium rest PET image will be obtained prior to a Dipyridamole stress test. Subjects will receive both Rubidium and technetium isotopes following the Dipyridamole stress, and will undergo first PET imaging and later SPECT imaging following the stress test. Patients will then go for cardiac catheterization as clinically ordered by their physician.