OBJECTIVES: The aim of this study was to investigate the correlation between myocardial ischemia detected by myocardial perfusion imaging (MPI) with single-photon emission computed tomography with intracoronary pressure-derived fractional flow reserve (FFR) in patients with multivessel coronary disease at angiography. BACKGROUND: Myocardial perfusion imaging can underestimate the number of ischemic territories in patients with multivessel disease. However, there are limited data comparing MPI and FFR, a highly accurate functional index of myocardial ischemia, in multivessel coronary disease. METHODS: Sixty-seven patients (201 vascular territories) with angiographic 2- or 3-vessel coronary disease were prospectively scheduled to undergo within 2 weeks MPI (rest/stress adenosine) and FFR in each vessel. RESULTS: In 42% of patients, MPI and FFR detected identical ischemic territories (mean number of territories 0.9 +/- 0.8 for both; p = 1.00). In the remaining 36% MPI underestimated (mean number of territories; MPI: 0.46 +/- 0.6, FFR: 2.0 +/- 0.6; p <0.001) and in 22% overestimated (mean number of territories; MPI: 1.9 +/- 0.8, FFR: 0.5 +/- 0.8; p <0.001) the number of ischemic territories in comparison with FFR. There was poor concordance between the ability of the 2 methods to detect myocardial ischemia on both a per-patient (kappa = 0.14 [95% confidence interval: -0.10 to 0.39]) and per-vessel (kappa = 0.28 [95% confidence interval: 0.15 to 0.42]) basis. CONCLUSIONS: Myocardial perfusion imaging with single-photon emission computed tomography has poor concordance with FFR and tends to underestimate or overestimate the functional importance of coronary stenosis seen at angiography in comparison with FFR in patients with multivessel disease. These findings might have important consequences in using MPI to determine the optimal revascularization strategy in patients with multivessel coronary disease. Copyright (c) 2010 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.