The purpose of this study is to see whether apadenoson is as effective as adenosine when used as a pharmacological stress agent in myocardial SPECT-imaging (SPECT-MPI)to detect defects in the supply of blood to the heart muscle (myocardial perfusion defects). The study will also look at whether apadenoson is better tolerated than adenosine when used in SPECT-MPI.

Adenosine is an effective vasodilator used in SPECT-Myocardial Perfusion Imaging (SPECT-MPI). However, it produces transient symptoms that are poorly tolerated by most subjects. This is a multi-center, randomized double-blind study to compare the tolerability and effectiveness of apadenoson to adenosine (Adenoscan®) in SPECT-MPI. Subjects who are clinical candidates for SPECT-MPI will be enrolled to undergo two sequential SPECT-MPI studies. The first study will use adenosine as the stress agent in approximately 1250 subjects. Eligible subjects will then be randomized in a 1:1 assignment ratio to receive a second SPECT-MPI using either adenosine or apadenoson as the pharmacologic stress agent, with the goal of obtaining a total of 670 subjects who complete both studies. The agreement of the results from the two adenosine:adenosine stress tests will be compared to that from the adenosine:apadenoson tests to assess efficacy. The incidence and intensity of commonly reported side effects will be compared to evaluate improved tolerability.

Inclusion Criteria:

• Referred for a clinically indicated rest/pharmacologic stress SPECT-MPI test
• High pretest probability (90% or greater) of CAD based on the ACC/AHA guidelines for relative risk, or past medical h/o CAD

Exclusion Criteria:

• Acute MI, new onset of ischemia or PCI within 30 days prior to SPECT-MPI at either Period 1 or Period 2; or CABG within 90 days prior to SPECT-MPI at either Period 1 or Period 2
• Active severe asthma or severe chronic obstructive pulmonary disease (COPD) which, in the Investigator's opinion, places the subject at risk for severe bronchoconstriction
• History or evidence of clinically significant cardiac condition and rhythm disorder, in the absence of a functioning permanently implanted pacemaker
• Hemodynamically significant valvular disease, outflow tract obstruction, or uncontrolled severe hypertension
• Known history of cerebral vascular accident or suspected transient ischemic attack within 30 days prior to signed informed consent
• Current significant medical, surgical, psychiatric, or other illness or pathology that could potentiate any adverse pharmacological event associated with an investigational drug