Implementing Myocardial Computed Tomographic Perfusion in a Community Hospital Setting

Inclusion Criteria: * Index CCTA. The patient must have a CCTA done for clinical indications within the 2 weeks prior to consent/enrollment, ordered by The Heart Group of Lancaster General Health. * Age greater than 18 years. * Lesion(s) requiring further testing. Upon review of the coronary CT angiogram, the interpreting physician (who was trained at the Johns Hopkins course for CTP imaging) finds at least one lesion that could benefit from further evaluation, specifically at least one stenosis of 50%-70%, or lesions with unclear stenosis severity suspected of being 50%-70%. * Referring physician agreement. The referring physician has been contacted and agrees that the patient can be approached for consent. * Informed consent. The patient is willing and able to provide informed consent. Exclusion Criteria: * CCTA complication. After an observation period of at least 20 minutes after the index CCTA, any evidence of MACE, allergy, or any other untoward clinical event that reduces CTP safety or suitability (as defined by attending physician) will exclude a patient from eligibility. * Contraindication to regadenosen according to LGH protocol (addendum 2). * Medical record of acute ischemia as evidenced on ECG or positive cardiac biomarkers in the interim between CCTA and CTP. Electrocardiographic evidence of acute ischemia includes acute STEMI (ST elevation equal to or greater than 1mm in two or more leads), ST segment depression and/or T wave inversion (not known to be old and thought to be evidence of ongoing ischemia). Positive cardiac biomarkers include elevated troponin, myoglobin, and/or creatinine phosphokinase MB fraction). * History of asthma or chronic obstructive pulmonary disease requiring bronchodilators or steroid therapy within the past 3 months. * Inability to tolerate beta blockers. * Atrio-ventricular block (Type II-III), prolonged QT interval or sick sinus syndrome. * Renal insufficiency (creatinine ≥1.6 and/or, GFR \< 60 ml/m) or renal failure requiring dialysis. * Atrial fibrillation or other markedly irregular rhythm. * Psychological unsuitability or extreme claustrophobia. * Pregnancy or unknown pregnancy status. * Clinical instability as deemed by the attending physician; including but not limited to: cardiogenic shock, hypotension (systolic blood pressure \< 90 mmHg), refractory hypertension (systolic blood pressure \> 180 mmHg), sustained ventricular or atrial arrhythmia requiring intravenous medications. * Use of Viagra or Cialis in the past 24 hours. * Known history of allergy or adverse reactions to x-ray dye, regadenoson or aminophylline. * Use of caffeine within the previous 12 hours (inactivates regadenoson). * History of severe aortic stenosis.