Regadenoson (Lexiscan), a low affinity agonist of the A2A adenosine receptor, increases coronary blood flow (CBF) and mimics the increase in CBF caused by exercise. Myocardial uptake of the radiopharmaceutical is proportional to CBF creating the contrast required to identify stenotic coronary arteries. It is a pharmacologic stress agent indicated for radionuclide myocardial perfusion imaging (MPI) in patients unable to undergo adequate exercise stress. The most common adverse reactions to Lexiscan are dyspnea, headache, flushing, chest discomfort, dizziness, angina pectoris, chest pain, and nausea. Methylxanthines, e.g., caffeine and theophylline, may interfere with the activity of Lexiscan. Aminophylline may be used to attenuate severe and/or persistent adverse reactions to Lexiscan.