The main clinical application of cardiac hybrid imaging so far has been the evaluation of coronary artery disease (CAD). It is well known that the angiographic severity of coronary lesion is a poor predictor of its hemodynamic significance (Gould and Johnson 2010; Tonino et al. 2010; Uren et al. 1994; White et al. 1984). Correspondingly, studies of computed tomographic angiography (CTA) have shown that only 30%–50% of stenoses with more than 50% luminal narrowing are associated with reversible perfusion defects on myocardial perfusion imaging (MPI). On the other hand, many patients with completely normal myocardial perfusion may have nonobstructive CAD (Gaemperli et al. 2007; Hacker et al. 2007; Schuijf et al. 2006).