Patients who come to the emergency room of Suburban Hospital in Bethesda, MD, because of chest pain may be asked to enroll in this study if they have not been diagnosed as having a heart attack. Participating patients will undergo a MRI scan as soon as emergency room doctors determine they are in stable condition. For this procedure, the patient lies on a table that slides into the MRI scanner-a large tubular machine with a magnetic field. During the scan, a contrast material is injected into the vein. This material brightens the image of the heart so that the blood flow can be seen. The scan will show if there are areas of heart muscle that received insufficient blood flow. A second scan will be done within 72 hours to look for coronary artery blockage that may require treatment. Patients will be followed by telephone 4 to 8 weeks after the scans and again 1 year after the scans to ask about any significant medical problems that may have occurred during those time periods.