This study will use phase contrast images obtained from patients during their clinically indicated CMR stress study to calculate myocardial perfusion reserve as the ratio of maximum myocardial blood flow to baseline blood flow - at the coronary sinus. Coronary sinus flow will be calculated by post-processing of images after the patient has left the scanner. In brief, the contour of the coronary sinus will be traced on the flow images throughout the cardiac cycle. Coronary sinus flow is calculated by integrating the momentary flow rate values from each cardiac phase over the entire cardiac cycle and multiplying by the mean heart rate during the acquisition. Patients will be followed for the occurrence of major adverse cardiac events (death, myocardial infarction, late revascularization, hospitalization for heart failure or unstable angina).