Pre-procedural Medications: In order to obtain high quality computed tomographic images with minimal motion artifacts, the goal heart rate is ≤ 65 beats per minute. This usually requires administration of beta-blocker medications before image acquisition. In addition, subjects with baseline low rates (> 65bpm) generally need a reduced dose of beta-blockers to blunt increases in rate during the MSCT scan due to anxiety and or reflex responses to contrast. The dose of initial oral beta-blocker will be determined based on resting heart rate at the time of exercise treadmill testing. For subjects with a baseline heart rate above 65bpm and blood pressure above 100/50, 100-150mg of short acting metoprolol will be prescribed by the investigator. Subjects will be instructed to ingest this medication approximately one hour before the scheduled outpatient MSCT scan. For subjects with heart rates above 50bpm and less than 65bpm and blood pressure above 100/50, 25-50 mg of oral short acting metoprolol will be prescribed by the investigator. Subjects will be instructed to ingest this medication approximately one hour before the scheduled outpatient MSCT scan. For subjects with a baseline heart rate < 50bpm, no metoprolol will be prescribed.