Study Design: This will be a prospective, open-label, comparative trial using MRI. Non-invasive MRI measurements of resting flow and flow at regadenoson stress will be obtained in each subject during a one hour MRI exam using our advanced MRI acquisition techniques. Sensitivity/specificity of regadenoson stress MRI will be determined using x-ray angiography as the standard. X-ray angiography will be done as standard-of-care, and is not an intervention of this clinical trial.