Regadenoson is stress agent approved by the FDA for use with myocardial perfusion imaging with technetium-99m single photon emission computed tomography (SPECT) in patients that are unable to exercise adequately. We would like to study Regadenoson in conjunction with Exercise Rubidium-82 positron emission tomography myocardial perfusion imaging (PET MPI). Regadenoson is not approved by FDA for use with Rubidium-82 PET MPI. Also, we would like to study a novel stress protocol of Regadenoson combined with symptom limited exercise stress (not FDA approved).