To exam the feasibility and accuracy of RTPE during vasodilator stress with 400micrograms of the A2A Receptor agonist Regadenoson for detection of significant coronary artery disease (CAD) in patients scheduled to undergo coronary angiography. Sensitivity, specificity , and accuracy of perfusion and wall motion analysis to identify a coronary stenosis> 50% in diameter by quantitive angiography will be analyzed