 Patients will have two 18-20 gauge intravenous lines placed, one preferably in an antecubital vein for contrast administration. The patient will be hydrated with normal saline intravenously 250 - 500 ml prior to CT scanning. The patient will lie supine on the scanner table and be attached to a 12 lead electrocardiographic monitor and an automated blood pressure monitor. Baseline ECG, heart rate, and blood pressure will be recorded and reviewed by one of the study investigators. Due to resultant artifacts from precordial leads, the 12 ECG leads and electrodes will be removed and rhythm monitoring will continue using the 3 lead system attached to the scanners monitoring system during scanning. A physician will be present at all times during adenosine infusion and CT imaging. Patients may receive an oral andor intravenous dose of metoprolol up to one hour prior to the CT. If the heart rate is 60 beats per minute, 75 mg max 80 mg of metoprolol will be given orally. If Heart rate remains 60 beats per minute at the scan acquisition then, intravenous beta blocker metoprolol, propranolol or landiolol 2.5 - 5.0 mg every 5 minutes will be administered to achieve a heart rate between 60 beats per minute as blood pressure tolerates under the supervision of a physician. Scout images for determining scanning range will be obtained in the anterior-posterior and lateral views. Patients with systolic blood pressure 110 will receive sublingual fast acting short lasting nitrates e.g. nitroglycerin, isosorbide dinitrate. Patients will then be asked to hold their breath approximately 10-15 seconds and non-contrast CT imaging will be performed starting just cranial to the coronary ostia and extending just caudal to the apex of the heart in order to obtain a coronary calcium score. CT angiogram will be performed to evaluate the coronaries and myocardial perfusion at rest. Blood pressure will be checked and intravenous adenosine infusion 0.14 mgkgmin will begin with continuous heart rate and rhythm monitoring. After 5 minutes of adenosine infusion, contrast-enhanced CT perfusion imaging will be performed during a 4-5 mlsec intravenous iodinated contrast ISOVUE-370 infusion. Total contrast dose for the entire protocol will not exceed 140 ml and will be based on patients body size. Patients will be asked to hold their breath during scanning. Immediately following completion of the scan, the adenosine infusion will be discontinued. A twelve lead ECG and blood pressure measurement will be repeated after discontinuation of adenosine and reviewed by a physician. Intravenous hydration will be continued during recovery with normal saline for a total volume for the entire post scan of 250 to 500 ml if deemed appropriate by the supervising physician. 