On the day of the MSCT scan and upon arrival to the Radiology Department, the subject will receive a peripheral upper extremity intravenous catheter, placed by a certified nurse in the Radiology Department. The subject’s baseline blood pressure and heart rate will be recorded. For subjects whose heart rate remains ≥ 65 beats per minute and blood pressure ≥ 100/50, intravenous metoprolol (5 mg aliquots every 2-5 minutes under close observation and continuous telemetric monitoring, up to 40 mg total) will be administered by a cardiology staff or fellow. Once satisfactory heart rate and blood pressure stability are established, subjects will undergo MSCT testing as listed below. However, if target heart rate is not achievable by this protocol, this is not cause for exclusion from the study, since feasibility and accuracy studies have shown that diagnostic scans can be obtained in many patients with higher heart rates with advanced scanners. Nitroglycerin, a coronary vasodilator, will be administered to all subjects (0.8 mg sublingually) approximately 1 minute before initiation of the MSCT scan to optimize image quality. Subjects will be queried regarding the recent use (within the previous 72 hours) of medications for erectile dysfunction (Cialis, Levitra and Viagra) on the day of the MCST scan since these drugs can interact with nitroglycerin to cause a potential life-threatening hypotensive effect. On the day of the scheduled MSCT scan, subjects who admit to have taken Cialis within the past 72 hours or Levitra / Viagra within the past 48 hours will not be allowed to undergo coronary MSCT angiography and will be rescheduled. Subjects will be instructed to withhold these medications for at least 3 days before the scheduled scan.