Caffeine's Effect on Regadenoson Administration With Single Photon Emission Computed Tomography (SPECT) Myocardial Perfusion Imaging (MPI)

Observe whether the administration of caffeine prior to regadenoson will affect the interpretation of test results in subjects with coronary artery disease (CAD) undergoing SPECT MPI

All subjects will undergo rest and stress scans. Those subjects who qualify by demonstrating at least 1 reversible defect, will undergo a third scan. All stress scans will involve the injection of regadenoson as the pharmacologic stress agent. Prior to the third scan, the subject will be administered blinded capsules of placebo or caffeine.

Eligibility Criteria:
Inclusion Criteria:

* Subject must have undergone a previous diagnostic study \[e.g., SPECT, echocardiography, magnetic resonance imaging (MRI), etc.\] for a clinical indication demonstrating evidence of reversible defects in ≥ 1 vascular segment, have had other stress testing within the past 3 months, or the subject's history suggests at least a 50% likelihood of CAD

  * If the previous diagnostic study shows only 1 reversible defect and it is in segment 17, another reversible defect will need to be present
* Subject with CAD must have an intermediate/low-risk for immediate intervention
* Subject must ingest caffeinated food or beverages regularly (at least the equivalent of one cup of caffeinated coffee daily)
* Subject must agree to not ingest any caffeine or other foods containing methylxanthine at least 24 hours prior to each study visit
* Subject must agree to abstain from eating solid food or drinking liquids other than water for at least 30 minutes prior to each study visit and 30 minutes following each study visit

Exclusion Criteria:

* Subject with documented myocardial infarction (MI) ≤ 30 days prior to enrollment
* Subject with history of percutaneous coronary intervention (PCI) ≤ 4 weeks prior to enrollment
* Subject with history of coronary artery bypass graft (CABG) ≤ 8 weeks prior to enrollment
* Subject has prior history of heart transplantation
* Subject has unstable angina, known severe left main coronary artery stenosis, severe heart failure, uncontrolled arrhythmias, symptomatic hypotension or severe hypertension (systolic blood pressure \< 90 or \> 180 mmHg, respectively), or \> 1st degree atrioventricular block in the absence of a functioning pacemaker
* Subject requires emergent cardiac medical intervention or catheterization
* Subject has a history of smoking, regardless of frequency, tobacco type or method of intake, or using any smoking cessation products, including but not limited to the nicotine patch or nicotine gum, within 3 months prior to first dose of regadenoson
* Subject is currently undergoing treatment with theophylline, or theophylline containing medications within 7 days prior to randomization (Day 3)
* Subject has a history of known or suspected bronchoconstrictive or bronchospastic lung disease \[e.g., asthma, wheezing, chronic obstructive pulmonary disease (COPD), etc.\]
* Subject has a history of diabetes associated with gastric disorders and/or emptying
* Subject has end stage renal disease (ESRD) with a GFR\< 15mL/min or currently undergoing dialysis for ESRD