Comparison of Quantitative MRI Perfusion Methods With Quantitative PET Perfusion Imaging

* Inclusion Criteria: * All participants will be over the age of 18 and able to provide consent * Both healthy and subjects with cardiac disease (including atrial fibrillation but not required) will be recruited. * Exclusion Criteria: * Critically ill patients, patients on ventilators, patients with unstable angina or with hypotension, asthmatics, and other patients whose medical care or safety may be at risk from undergoing an MRI examination will be excluded. * Patients with claustrophobia will also be excluded from the study if this cannot be controlled with standard methods (valium or benadryl). * Patients with contraindication to MRI (pacemaker, metal implants, or certain types of heart valves), * pregnant patients, minors, mentally disabled patients and prisoners will be excluded from this study. (All criteria apply to patients and normal volunteers). * Gadolinium nephrotoxicity will be addressed by having patients with abnormal kidney function (GFR\<30) excluded from the study due to the (very small) risk associated with gadolinium contrast agents. This threshold may be modified, depending on practices determined by the Radiology Department and the IRB. * Patients with a known allergy or contraindication to Adenosine and/or Regadenoson will be excluded from stress (hyperemia) cohorts. * All participants that will receive a stress agent will refrain from consuming caffeine for at least 12 hours prior to each study