Objectives: This study sought to determine whether regadenoson induces left ventricular perfusion defects of similar size and severity as seen with adenosine stress. Background: Total and ischemic left ventricular perfusion defect size predict patient outcome. Therefore, it is important to show that newer stressor agents induce similar perfusion abnormalities as observed with currently available ones. Methods: The ADVANCE MPI 2 (Adenosine versus Regadenoson Comparative Evaluation for Myocardial Perfusion Imaging) study was a prospective, double-blind, randomized trial comparing image results in patients undergoing standard gated adenosine single-photon emission computed tomography (SPECT) myocardial perfusion imaging who were then randomized in a 2:1 ratio to either regadenoson (N = 495) or a second adenosine SPECT (N = 260). Quantitative SPECT analysis was used to determine total left ventricular perfusion defect size and the extent of ischemia. Quantification was performed by a single observer who was blinded to randomization and image sequence. Results: Baseline gated perfusion results were similar in patients randomized to adenosine or regadenoson. No significant differences in total (11.5 ± 15.7 vs. 11.4 ± 15.8, p = 0.88) or ischemic (4.8 ± 9.2 vs. 4.6 ± 8.9, p = 0.43) perfusion defect sizes were observed between the regadenoson and adenosine groups, respectively. Linear regression showed a close correlation between adenosine and regadenoson for total (r = 0.97, p < 0.001) and ischemic (r = 0.95, p < 0.001) left ventricular perfusion defects. Serial differences in total (-0.03 ± 3.89 vs. -0.13 ± 4.16, p = 0.73) and ischemic (0.15 ± 4.08 vs. 0.25 ± 3.81, p = 0.74) perfusion defect size and left ventricular ejection fraction (0.12 ± 0.32 vs. 0.15 ± 0.35, p = 0.27) from study 1 to study 2 were virtually identical in patients randomized to regadenoson versus adenosine, respectively. The good correlation between serial adenosine and regadenoson studies regarding total (0.41 ± 5.43 vs. 0.21 ± 5.23, p = 0.76) and ischemic (0.17 ± 5.31 vs. 0.23 ± 6.08, p = 0.94) perfusion defects persisted in the subgroup of 308 patients with an abnormal baseline SPECT. Conclusions: Applying quantitative analysis, regadenoson induces virtually identical scintigraphic results as adenosine regarding the size and severity of left ventricular perfusion defects and the extent of scintigraphic ischemia. © 2009 American College of Cardiology Foundation.